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Dissertations / Theses on the topic 'Elongation of the material'
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1
Kataoka, Kazuya. "Alginate, a bioresorbable material derived from brown seaweed, enhances elongation of amputated axons of spinal cord in infant rats." Kyoto University, 2004. http://hdl.handle.net/2433/147554.
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McLaughlin, Jacob Ryan. "Control of swelling, electrochemical, and elongation properties of photopolymers through the modification of structure." Diss., University of Iowa, 2018. https://ir.uiowa.edu/etd/6205.
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Modifying photopolymer structure on the molecular and nanoscale level permits tailoring materials for use in a wide variety of applications. Understanding the fundamentals behind polymer structure at these levels permits the control of material properties. This work gains insight into the modification of structure on two levels, the nanoscale by use of structure templates and the molecular scale through the modification of polymer network formation.
Lyotropic liquid crystals (LLCs) are a type of self-assembling surfactant system, which in combination with photopolymerization can be used to template ordered nanostructure within polymer materials. This structure can be controlled and utilized to influence the properties of a polymer material. This research examines materials used as templating agents and the types of nanostructures that may be obtained. Additionally, their effects upon the LLC templating process and material properties is determined. Structured polymers are created using LLC templates in pursuit of materials for use in water purification processes and electrochemical devices. Through a more complete understanding of the fundamentals of the templating process, the work presented here extends the LLC templating technique to a greater variety of materials and applications in the water remediation and energy storage fields.
The second portion of this research is the use of reversible addition fragmentation chain transfer (RAFT) to modify photopolymer networks. RAFT agents are utilized to control the propagation reaction to create networks with increased homogeneity between network crosslinks. By increasing the uniformity of the polymer network, increases in polymer elongation and toughness as well as decreases in polymer modulus are observed. The effects of RAFT agent addition on the network formation and the final properties of the photopolymer is examined. By understanding the mechanisms behind this modification technique, photopolymers can be extended into new applications where increased elongation and toughness is valued.
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V, Venkataramanan. "Material characterization in elongational flows /." The Ohio State University, 1997. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487943610784079.
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Hwang, Fengtai Mark. "Material characterization of agricultural and industrial solutions and melts in elongational processes /." The Ohio State University, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=osu1488202171194385.
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Ahirwal, Deepak. "Large deformation shear and elongation rheology of polymers for electrospinning and other Industrial Processes." Phd thesis, Université de Strasbourg, 2013. http://tel.archives-ouvertes.fr/tel-01065971.
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The goals of this thesis are the characterization of polymer melts using mainly non-linear shear and extensional rheological techniques. The fabrication of scaffolds with excellent physical and mechanical properties using solution electrospinning technology for tissue engineering applications and the development of melt electrospinning equipment to facilitate the fabrication of solvent free scaffolds. To achieve the first goal, we focused on the characterization of entangled polymer melts in the linear and nonlinear viscoelastic regimes. The influence of molecular weight, Mw, molecular weight distribution (MWD), long-chain branching (LCB) and addition of particles to the polymer matrix on polymer melt properties were investigated using shear and extensional rheological techniques. The resulting structure-property relationships were established using newly introduced mechanical parameters under large amplitude oscillatory shear (LAOS) flow.
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ABDU, ALINE AMARAL QUINTELLA. "ELONGATIONAL BEHAVIOR OF COMPOSITE THERMOPLASTIC MATERIALS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2007. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=11520@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOOs materiais termoplásticos compósitos, tais como o polipropileno reforçado com fibras de vidro curtas, são usados cada vez mais em diversos setores industriais. O reforço da fibra de vidro é uma forma utilizada para melhorar as propriedades mecânicas dos termoplásticos, devido ao elevado módulo das fibras e à melhor adesão entre as fibras e a matriz polimérica. No entanto, há poucas informações referentes às propriedades desses fluidos na literatura. No presente trabalho, um estudo das propriedades cisalhantes e elongacionais do polipropileno reforçado com fibras de vidros curtas é apresentado. As viscosidades cisalhantes e elongacionais foram obtidas em um reômetro capilar através da medição da queda de pressão na entrada convergente de um capilar axissimétrico. Utilizaram-se duas geometrias diferentes na entrada do capilar, para a obtenção dos dados experimentais: as geometrias semi-hiperbólica convergente e cônica convergente. Neste último, a viscosidade elongacional foi obtida a partir da queda de pressão na entrada, utilizando as análises de Cogswell e Binding. Simulações numéricas foram realizadas com o objetivo de investigar o comportamento do polipropileno em um processo de extrusão. As equações de conservação de massa e quantidade de movimento foram resolvidas utilizando o método dos elementos finitos a partir do programa comercial Polyflow (Ansys). Para modelar o comportamento da mecânico viscoelástico do polipropileno foram utilizados os modelos de Maxwell, Oldroyd-B e Phan-Thien Tanner (PTT), no entanto a comparação entre os resultados numéricos e os experimentais obtidos no reômetro capilar não apresentaram concordância satisfatória.
Composite thermoplastic materials, like glass fiber reforced polypropropylene, are used increasingly in several industries. In particular, glass fiber reinforcement is used to improve the mechanical properties of thermoplastics, due to the high fiber modulous and to the better adesion between the fibers and the polymeric matrix. However, few data of material properties of these fluids are avaiable in the literature. In this work, a study of shear and elongational properties of a commercial short glass fiber reinforced polypropylene is presented. The shear and elongational viscosities were obtained using the pressure drop measured at a capillary rheometer, with axisymmetric converging dies. Two different die geometries were used: semihyperbolically convergent dies and conical convergent dies. In the last case, the elongational viscosity was obtained using the Cogswell and Binding analysis. Numerical simulations were also performed, to investigate the flow field through the extrusion die process, and to evaluate the pressure drop and elongational viscosity. The conservation equations of mass and momentum were solved via the finite element method, using the commercial program POLYFLOW (Ansys). The Maxwell, Oldroyd B and Phan Thien-Tanner (PTT) constitutive equations were used to model the viscoelastic mechanical behavior of Polypropylene, but the comparison between numerical results and experimental data obtained from the capillary rheometer did not show good agreement.
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Kangas, J. (Jarmo). "Outcome of total Achilles tendon rupture repair, with special reference to suture materials and postoperative treatment." Doctoral thesis, University of Oulu, 2007. http://urn.fi/urn:isbn:9789514284342.
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Abstract
The purposes of the present research were to compare the outcome after Achilles tendon rupture repair in two postoperative regimens, to compare Achilles tendon elongation in two postoperative treatment methods, to compare the effects of two postoperative methods on motor performance aspects such as simple reaction time, choice reaction time, speed of movement, foot tapping speed and coordination, to test the mechanical properties of the recently developed poly-L/D-lactide (PLDLA) sutures and Maxon® sutures when implanted in the Achilles tendons of rabbits, and to study the histological tissue reactions and biodegradation of these sutures under the same conditions.
Isokinetic calf muscle strength scores at the last control check-up were excellent in 56% of the patients in the early motion group, good in 32%, fair in 8%, and poor in 4%, whereas the scores in the cast group were excellent in 29% of cases, good in 50% and fair in 21%. The ankle performance scores were excellent or good in 88% of the patients in the early motion group, fair in 4% and poor in 8%, whereas the scores in the cast group were excellent or good in 92% of cases and fair in 8%. No significant differences were seen between the two groups at 3 months and at the last control checkups with regard to pain, stiffness, subjective calf muscle weakness, footwear restrictions, range of ankle motion, isokinetic calf muscle strength or overall outcome. The complications included 1 re-rupture in the early motion group and 1 deep infection and 2 re-ruptures in the cast group.
AT elongation occurred in both groups, but was somewhat less marked in the early motion group. The AT elongation curves rose at first and then fell slowly in both groups. The patients who had less AT elongation achieved a better clinical outcome. AT elongation did not correlate significantly with age, body mass index or isokinetic peak torques.
The recovery of motor performance functions such as simple reaction time, choice reaction time, speed of movement, foot tapping speed and coordination did not depend on the two postoperative regimens. The motor functions of the operated leg had obviously recovered to the level of the non-operated leg 12 weeks after the operation.
Sutures made of PLDLA were used successfully for Achilles tendon repair in rabbits. There was no significant difference between the in vitro and in vivo tensile strength retention of the sutures. By comparison with Maxon®, PLDLA was found to have a lower initial tensile strength but more prolonged strength retention. The breaking strength values of the Achilles tendons repaired with sutures of these types were not significantly different at 6 weeks.
Intratendinous PLDLA sutures formed a thinner fibrous capsule during the 12-week follow-up period than did Maxon® sutures of the same diameter. The suture materials had not been totally absorbed by 12 weeks.
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Langer, Jiří. "Stanovování mechanických vlastností lehkých kovů a jejich slitin a kompozitů pomocí protlačovacích zkoušek na miniaturních discích." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2014. http://www.nusl.cz/ntk/nusl-231481.
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The aim of diploma thesis is estimate mechanical properties (yield strength, maximum strength and elongation) of light alloys by means of SPT. For the experiments were selected aluminium alloys (Al 2024, Al 6082 T6, Al 7020 and NASA 398) magnesium alloys (MgZnMn, AZ31, AZ61) and composites (AZ91 + 20 % saffilu a Al + Al4C3). Theoretical part of this thesis is focused on analysis of conversion formulas, which were made from SPT data and conventional testing. Experimental part is dedicated to evaluation of experimental data and critical analysis validity of conversion formulas. In this part of thesis is discused the problematics of reproducibility methodology of SPT.
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Chen, Menglin. "Studies of Translation Elongation and its Relationship to Transcription Elongation in Bacteria." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1586468314499281.
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Buchan, J. Ross. "Control of translation elongation." Thesis, University of Aberdeen, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.440061.
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Previous pilot studies had identified markedly biased usage of codon pairs within ORFs of E. coli, S. cerevisiae and C. albicans, suggestive that codon pair usage may generally regulate translation elongation in some way. In this work, comprehensive analyses of coding sequences of multiple genomes revealed that biased usage of codon pairs is universal, and that a tetranucleotide sequence spanning the last position of the P-site codon and all nucleotides in the A-site codon underlies this selection. Furthermore, in S. cerevisiae, S. pombe, B. subtilis and members of the gamma-protobacteria family (including E. coli), interactions between the A-site tRNA and the 3rd position nucleotide of the P-site codon, act as a key selective force driving codon pair selection. Analysis revealed A-site tRNA sequences in the anticodon stem loop and the amino acid acceptor stem that positively and negatively contribute to codon pair selection in a variety of prokaryotes. tRNA availability, coupled with usage of codons in ORFs, is yet another key regulation point in elongation. Previous studies in prokaryotes have suggested that the encounter of repeated runs of rare codons by elongating ribosomes can lead to processivity errors (e.g. ribosomal drop off, frameshifting) due to the depletion of charged tRNA levels. However, the effects of such ‘polycodon’ sequences upon eukaryotic elongating ribosomes are unknown. In this work, reporter mRNAs containing both rare and common polycodon sequences were expressed and the consequential effects on gene expression observed. Several key findings emerged from this work. Firstly, repeated runs of rare and common codons inserted in frame between two fused reporter genes caused reduced expression of the 3’ ORF reporter activity. Evidence was obtained indicating a novel proteolysis event acted between the two reporter enzyme domains, as well as preliminary evidence for ribosomal drop off. Finally, a novel +1 frameshifting motif involving CGG polycodon sequences was identified.
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Mareschal, Olivier. "Étude d'un résonateur piézoélectrique à ondes acoustiques de volume en technologie film mince." Phd thesis, Université Paris-Est, 2011. http://tel.archives-ouvertes.fr/tel-00789852.
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Le résonateur étudié s'insère dans un projet industriel porté par NXP Semiconductors. L'objectif est la réalisation d'un résonateur MEMS RF intégrable en vue de remplacer le quartz dans certaines applications. La compatibilité du procédé de fabrication avec les technologies utilisées par la société et le faible coût de production représentent les principaux enjeux du projet. Le résonateur TFEAR (Thin Film Elongation Acoustic Resonator) est un barreau, constitué d'une superposition de couches minces de type Métal/AlN/Métal. Les propriétés piézoélectriques du nitrure d'aluminium (AlN) sont ainsi exploitées : l'application d'un champ électrique alternatif, parallèle à l'épaisseur du barreau, entraîne une propagation d'ondes acoustiques suivant sa longueur. Les dimensions des résonateurs fabriqués correspondent à des fréquences de résonance comprises entre 10MHz et 50MHz. Cette thèse s'intéresse la modélisation et à la caractérisation électrique du résonateur TFEAR. Les modèles théoriques sont développés par simulations numériques 3D et par calculs analytiques 1D. Le comportement électrique du TFEAR est décrit par un schéma équivalent, dont les éléments sont exprimés en fonction des paramètres physiques et des pertes des matériaux le constituant. Un facteur de qualité de 2250 sur un TFEAR résonant à 25,79MHz et dont la résistance motionnelle est de 2,1 kOhms a été relevé. Ces mesures ont été complétées par la caractérisation des paramètres physiques de la couche piézoélectrique. Par exemple, des valeurs de coefficient piézoélectrique d33f atteignant 2,6 pm/V ont été relevées (pour un maximum théorique de 3,93 pm/V)
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Magnusson, Mattias, and Christian Tolstrup. "Enkel mätning av elongation vid dragprov." Thesis, KTH, Tillämpad maskinteknik (KTH Södertälje), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-155669.
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Zadravec, Damir. "Metabolic Significance of Fatty Acid Elongation." Doctoral thesis, Stockholm : Department of Physiology, Stockholm University, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-34815.
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Diss. (sammanfattning) Stockholm : Stockholms universitet, 2010.At the time of the doctoral defence, the following papers were unpublished and had status as follows: Paper 3: Manuscript. Paper 4: Manuscript. Paper 5: Submitted. Paper 6: Manuscript. Härtill 6 uppsatser.
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Carlson, Erik James. "Vertebral artery elongation during whiplash trauma." [New Haven, Conn. : s.n.], 2008. http://ymtdl.med.yale.edu/theses/available/etd-11212008-114040/.
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Kettenberger, Hubert. "Structure of the Complete RNA Polymerase II Elongation Complex and its Interaction with the Elongation Factor TFIIS." Diss., lmu, 2005. http://nbn-resolving.de/urn:nbn:de:bvb:19-39070.
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Smitter, Luis Manuel. "Study of the interactions between poly(ethylene oxide) and anionic surfactants in elongational flow." Diss., The University of Arizona, 2001. http://hdl.handle.net/10150/279813.
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The rheology of polymer solutions is important in a wide variety of applications. In particular, solutions of high-molecular-weight, flexible polymers exhibit an increase in their apparent extensional viscosity with strain rate under extensional flow conditions. This extension thickening is due to formation of transient entanglements of polymer molecules. Certain commercial fluids contain both polymers and surfactants that might interact at the molecular level. These interactions affect the conformation of the polymer chain and, therefore, the rheological behavior of the solution. For instance, addition of anionic surfactants to solutions of nonionic polymers is known to induce increases in the shear viscosity of aqueous solution. This work investigates the behavior of aqueous solutions of a high-molecular-weight poly(ethylene oxide) (PEO), a nonionic, flexible polymer, and the anionic surfactants sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS) and a commercial alpha-olefin sulfonate (AOS) in extensional flows. The extensional rheology of polymer/surfactant solutions is studied in an opposed-jets device, which generates a flow field close to uniaxial extension. For PEO/SDS mixtures, the results show that formation of micellar aggregates of SDS along the PEO chains results in an increase in the strength of extension thickening of PEO solutions by promoting intermolecular interactions between polymer chains. The minimum PEO concentration required to form intermolecular entanglements is substantially reduced in the presence of micellar aggregates. In solutions containing NaCl, intramolecular interactions are observed at low PEO concentrations. These reduce the strength of extension thickening. Addition of a co-solvent is investigated. The presence of alcohols in the aqueous solutions affects their rheology by changing the solvent nature for both PEO and SDS. In particular, n-octanol promotes aggregation of SDS along the PEO chains, enhancing intermolecular network formation in extensional flow. Results with mixtures of PEO with sulfonated surfactants (SDBS and AOS) show that both intermolecular and intramolecular interactions are promoted by these surfactants, depending on PEO concentration and molecular weight. The effect of ageing on these polymer/surfactant systems was studied. In extensional flows, extension thickening is suppressed in solutions of PEO with SDBS or AOS over a few-day period, whereas PEO and PEO/SDS solutions show no change.
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Pärlstrand, Anders. "Ultrasonic measurement and analysis of screw elongation." Thesis, KTH, Hållfasthetslära (Avd.), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-232519.
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Based on the customers' increasing demands on the precision of the preload in a screw joint Atlas Copco is investigating the opportunity to integrate ultrasonic technologies in their industrial tools in order to be able to measure the screw elongation and thereby preload. The preload in a screw joint is important when trying to optimize the joint in terms of weight and life time. The ultrasonic technology for preload measurements has two large advantages; the technique requires only access to the screw head and it is completely independent of the friction in the joint which enables more accurate measurements of the preload. In ultrasonic preload measurements the time of flight is measured (i.e. time for ultrasonic waves to travel through the screw). The time can be transformed into length and elongation by use of the sound velocity. Of importance in this calculation is to take the so called acoustoelastic effect into account which predicts a lower longitudinal wave velocity with increasing tensile stress. The purpose of this master thesis is to develop a method that can predict screw elongations from ultrasonic measurements. Finite element simulations showed that the acoustoelastic ultrasonic constant only depend on the ratio between the clamp length and the screw diameter up to a certain degree of accuracy. A function of type =∙ ∙ where a, b and c are real-valued constants and = is the clamp length () divided by the screw diameter () fits the data well. However, the ultrasonic measurements showed some deviations from the theoretical predictions.
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Ying, Lanqing. "Studies on Translation Elongation and its Fidelity." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu153054014550459.
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Hatch, Victoria. "Transcriptional elongation is important for neural crest development." Thesis, University of East Anglia, 2013. https://ueaeprints.uea.ac.uk/48100/.
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Neural crest cells are a multipotent cell population, which migrate from the dorsal neural tube in early vertebrate development throughout the embryo to form a variety of cell types including pigment cells, craniofacial cartilage and sensory neurons [1, 2]. Here I show that the small molecule compound leflunomide is able to inhibit neural crest specification genes. Leflunomide exerts its actions by inhibiting pyrimidine synthesis and therefore RNA transcription [4]. Neural crest genes are thought to be actively transcribed and like many embryonic stem cell genes may undergo an increased level of transcriptional pausing and subsequent elongation rendering them more sensitive to the effect of leflunomide [3, 5]. I have gone on to show that components of the transcriptional elongation regulatory machinery, Cdk9 and CyclinT1 of the P-TEFb complex are also able to regulate neural crest specification. In particular the expression of the protooncogene c-Myc and c-Myc responsive genes are affected. c-Myc has been previously implicated in embryonic stem cell transcriptional elongation and also is well characterised to play a role in neural crest specification [6]. We postulate that regulation of c-Myc expression at the level of transcriptional elongation is important for the correct temporal and spatial development of the neural crest.
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Yankulov, Krassimir Yankov. "Regulation of transcriptional elongation by RNA polymerase II." Thesis, Open University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387189.
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Devaraj, Aishwarya. "Molecular Studies of the Fidelity of Translation Elongation." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1300816926.
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Welcsh, Piri Louise. "Cloning and characterization of elongation factor G genes /." The Ohio State University, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487777170406846.
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Ryu, Deug-Soo. "Rheo-Optical Studies on Polymers in Elongation Process." Kyoto University, 2001. http://hdl.handle.net/2433/150655.
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Bartish, Galyna. "Elongation factor 2 : a key component of the translation machinery in eukaryotes : properties of yeast elongation factor 2 studied in vivo /." Stockholm : Wenner-Gren Institute for Experimental Biology, Stockholm university, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-7733.
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Molloy, David P. "Spectroscopic studies on elongation factor Tu : an approach to the characterisation of the kinetic events during the elongation cycle of protein biosynthesis." Thesis, University College London (University of London), 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.277862.
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Schmidt, Thorsten. "Human CPAP and CP110 in centriole elongation and ciliogenesis." Diss., lmu, 2010. http://nbn-resolving.de/urn:nbn:de:bvb:19-130467.
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Gile, Gillian Heather. "Molecular evolution of the eukaryotic translation elongation factor, EFL." Thesis, University of British Columbia, 2009. http://hdl.handle.net/2429/11588.
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The eukaryotic translation elongation factor EFL (for EF-Like) is a paralogue of the better-known elongation factor 1-alpha (EF-1α), which brings aminoacyl-tRNAs to the ribosome during translation. This essential protein was thought to be ubiquitous in eukaryotes until the recent discovery of EFL in a small number of diverse, mainly unicellular, eukaryotic organisms that were found to lack EF-1α. Because of the great evolutionary distances between EFL-encoding lineages and the near mutual exclusivity of the two proteins, the observed complex distribution of EFL was initially attributed entirely to multiple lateral gene transfers. In the enclosed chapters, the distribution of EFL was characterized in more detail in four distantly related eukaryotic lineages at both fine and broad taxonomic scales in order to better understand the effects that endosymbiotic gene transfer, differential loss, and lateral gene transfer have had on the molecular evolution of EFL. Endosymbiotic transfer of EFL was detected in the chlorarachniophytes, a group of algae whose secondary plastids retain a vestigial nucleus, known as a nucleomorph, in their reduced eukaryotic cytoplasm, known as the periplastid compartment (PPC). The endosymbiotically transferred EFL carries a bipartite targeting sequence similar to those of plastid-targeted proteins in this group and to plastid- and PPC-targeting sequences in cryptomonads to direct it to the PPC, suggesting similarities in the way these two lineages have solved their shared challenge of targeting to complex plastids with nucleomorphs. No clear phylogenetic evidence for lateral transfer of EFL has yet emerged; rather, differential loss of EFL and EF-1α from an ancestral state of co-occurrence was characterized in euglenozoans and detected in publicly available data from heterokonts and opisthokonts, unexpectedly revealing a significant role for this process in shaping the complex distribution of EFL and EF-1α. This finding serves as a cautionary reminder that adequate taxon sampling and a robust organismal phylogenetic hypothesis are crucial in order to correctly infer lateral gene transfer.
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Sanderson, Lee Edward. "The tRNA affinity and specificity of elongation factor Tu." Diss., Connect to online resource, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3239403.
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Smurthwaite, Lyn. "Molecular studies on a putative human mitochondrial elongation factor." Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321998.
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Banzhaf, Manuel. "Characterisation of the cell elongation complex in Escherichia coli." Thesis, University of Newcastle Upon Tyne, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.519638.
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Derbyshire, Paul. "The cell wall and cell elongation in Arabidopsis seedlings." Thesis, University of East Anglia, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251441.
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The primary cell wall of dicotyledenous plants is comprised of approximately equal parts cellulose, cross-linking glycans, and pectin, with a relatively minor fraction of protein. The role that pectin may play in regulating cell elongation was studied in two systems in Arabidopsis seedlings; the primary root with its well-defined zone of elongating cells, and the hypocotyl that grows almost exclusively by cell elongation. A collection of mutants affected in root (cob-1, cob-3, lit-1 (rsw2), qui-1 (prcl-9), sab-1, shr-2) and hypocotyl (gal-3, gai) elongation was used to identify altered pectin phenotypes that correlated with the growth phenotypes. FT-IR microspectroscopy was used to show that roots and hypocotyls affected in cell elongation have pectin with lower degree of esterification (DE) values compared to wild-type. This was quantified and confirmed by chemical assays. DE is unchanged where cell elongation is increased by GA- and dark-induced growth, suggesting that a threshold of DE may exist that is permissive for growth, but below which reduced values of DE correlate with reduced elongation. The cob-1 mutant was studied in more detail, and found to have very low DE values in the region of greatest cellulose deficiency, together with thickened walls and other compositional changes. Other cellulose-deficient mutants (qui-1, lit-1) were similarly affected, suggesting that enrichment of the wall with pectin of low DE is used to conserve wall strength. Analysis of GA-deficient mutants gave some evidence that galactan side-chains, and to a lesser extent arabinan sidechains of RG-I may be required throughout the wall for elongation, and that the outer wall of roots and hypocotyls may be growth-limiting. Thinning of the cell wall correlates with hypocotyl length, suggesting that biosynthesis does not keep pace with elongation. Finally, root and hypocotyl cell walls have different DE values, suggesting that the properties of pectin in these systems may vary with different wall composition. Various mechanisms by which pectin DE may become limiting to the rate of cell elongation are proposed. DE is regulated by pectin esterases, which in Arabidopsis comprises a large gene family. To test the hypothesis that pectin esterification is limiting to cell elongation, four transposon insertion mutants in putative pectin esterases were screened for cell elongation and wall phenotypes, with the prediction that higher DE values in the mutant walls might result in increased growth. Under various conditions in the different mutants, DE was both raised and lowered and cell elongation promoted and inhibited. To avoid problems of genetic redundancya nd the absence of functional characterisation in this family, a PME with demonstrated biochemical activity from Aspergillus aculeatus was over-expressed in Arabidopsis and 30 transgenic lines generated. However, the phenotypes of these plants have not been analysed.
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Vezzaro, A. "Studies on axial elongation and segmentation in vertebrate embryos." Thesis, University College London (University of London), 2012. http://discovery.ucl.ac.uk/1348912/.
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The vertebrate body is segmented along the anteroposterior axis into repetitive structures, the vertebrae, which derive from embryonic precursors called somites. During development, periodic somite formation is driven by a molecular oscillator, the segmentation clock. Segmentation and elongation of the body axis depend on a population of progenitor cells located at the tail end of the embryo that contributes to axial tissues, including somitic tissue, until the entire embryonic body and the correct number of somites is produced. Although much is known about somite production, it is not known how segmentation and axial elongation come to an end. In this thesis, I show that termination of chick axial elongation is associated with decline of signals required for maintenance of progenitor cells, implying that downregulation of these signals triggers depletion of the progenitors. I also show that somite formation decreases as axial elongation comes to an end, suggesting that slow down of the segmentation clock causes somite formation to cease. I have also explored whether the dose of specific genes is limiting in determining the final somite number in mouse, and I have found that heterozygous mutations of selected genes of the Wnt signalling pathway form fewer somites, indicating that Wnt gene activity might be limiting in controlling the definitive somite number. I have also investigated the role of Greb1, a gene that our laboratory identified as being selectively expressed in the tail region where progenitors reside. I provide evidence that Greb1 controls axial morphogenesis of the zebrafish embryo by regulating movements required for normal convergence and extension of the embryonic axis during gastrulation. My results possibly provide a link between progenitor contribution to axial elongation and cell movements in the tail.
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Lin, Chengqi. "The super elongation complex (SEC) in development and disease." Thesis, Open University, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.594747.
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Chromosomal translocations involving the mixed lineage leukemia (MLL) gene are associated with infant acute leukemia. There are a large number of translocation partners of MLL that share very little sequence similarities, yet their translocations into MLL result in the pathogenesis of leukemia. To define the molecular reason why these translocations result in leukemogenesis, I purified several of the commonly occurring MLL chimeras and identified a novel Super Elongation Complex (SEC) associated with all chimeras purified. SEC consists of the RNA Pol II elongation factors ELLl -3, P-TEFb, and several frequent MLL-translocation partners. SEC is one of the most active P-TEFb complexes and is required for the proper expression ofMLL chimera target genes and the oncogene, MYe, 1 suggesting that the regulation of transcription elongation checkpoint control (TEeC) by SEC could play essential roles in leukemia. Paused Pol II has been proposed to be associated with loci that respond rapidly to environmental stimuli. My studies in mouse ES cells demonstrated that SEC is required for rapid transcriptional activation of genes, many of which contain paused Pol II. However, SEC is also required for the activation of the Cyp26aJ gene, which does not contain detectable Pol II, yet responds much more rapidly to retinoic acid than those paused genes, suggesting that paused Pol II is not a prerequisite for rapid gene activation. Furthermore, EIl3, a member of the ELL fami ly of proteins, predominately occupies poised, active, and inactive enhancers of many developmental genes in ES cells. E113's association with enhancers is required for setting up proper Pol II occupancy at the promoter-proximal regions of neighboring genes, providing a yet to be discovered mechanism for the transition from El13's presence at poised enhancers in ES cells to E112 's role in the release of paused Pol II during gene activation.
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Innes, Shona L. "mRNA secondary structure melting during translation elongation in yeast." Thesis, University of Aberdeen, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.248593.
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Two assay systems were designed and constructed in this study in order to investigate mRNA secondary structure melting during translation elongation in S. cerevisiae. The first, where stable secondary structures were placed within a lacZ reporter mRNA, was used to demonstrate that such structures are resolved efficiently, as the insertion of a stable stem-loop of -66 kcal/mol into the lacZ coding region only reduced translation efficiency by 40%. It was further demonstrated that the effect of secondary structures in open reading frames are not additive, as two stem-loops of -45 kcal/mol adjacent to one another did not decrease translation efficiency, to the extent expected of a single stem-loop of -90 kcal/mol. The L-A d.s. RNA virus RNA pseudoknot had no effect on translation elongation. A second assay, based on -1 frameshifting upstream of RNA secondary structure elements was used to test candidate genes for a role in mRNA secondary structure melting during translation elongation. It was demonstrated that two cytoplasmic RNA helicases, Ded1p and Dbp5p are not involved in this process. In contrast to previous work (Cui, et. al., 1996; EMBO 15:5726-5736) this study revealed that Upf1p, an RNA helicase involved in nonsense-mediated decay, played no role in -1 ribosomal frameshifting. Environmental effects on mRNA secondary structure melting were investigated by measuring secondary structure melting at 18oC, using the -1 frameshift assay. Contrary to expectations, -1 frameshifting was not enhanced by low temperature, perhaps because a helicase-like activity is induced at 18oC. Proteomic analysis revealed that increased levels of Gdh1p are associated with polyribosomes at 18oC compared to 37oC. Gdh1p interacts with Lsm1p, a component of an mRNA decapping complex, in a two-hybrid screen.
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Goyal, Akanksha, Riccardo Belardinelli, Cristina Maracci, Pohl Milon, and Marina V. Rodnina. "Directional transition from initiation to elongation in bacterial translation." Oxford University Press, 2015. http://hdl.handle.net/10757/579679.
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The transition of the 30S initiation complex (IC) to the translating 70S ribosome after 50S subunit joining provides an important checkpoint for mRNA selection during translation in bacteria. Here, we study the timing and control of reactions that occur during 70S IC formation by rapid kinetic techniques, using a toolbox of fluorescence-labeled translation components. We present a kinetic model based on global fitting of time courses obtained with eight different reporters at increasing concentrations of 50S subunits. IF1 and IF3 together affect the kinetics of subunit joining, but do not alter the elemental rates of subsequent steps of 70S IC maturation. After 50S subunit joining, IF2-dependent reactions take place independent of the presence of IF1 or IF3. GTP hydrolysis triggers the efficient dissociation of fMet-tRNAfMet from IF2 and promotes the dissociation of IF2 and IF1 from the 70S IC, but does not affect IF3. The presence of non-hydrolyzable GTP analogs shifts the equilibrium towards a stable 70S–mRNA–IF1–IF2–fMet-tRNAfMet complex. Our kinetic analysis reveals the molecular choreography of the late stages in translation initiation.Boehringen Ingelheim Fonds and the G¨ottingen Graduate School for Neurosciences, Biophysics, and Molecular Biosciences (to A.G.); Max Planck Society and grants of the Deutsche Forschungsgemeinschaft (to M.V.R.); Peruvian Programa Nacional de Innovaci ´on para la Competitividad y Productividad [382-PNICP-PIBA-2014 (to P.M.)]. Funding for open access charge: Max Planck Society.
Revisión por pares
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Sen, Rwik. "REGULATION OF EUKARYOTIC TRANSCRIPTIONAL ELONGATION AND ASSOCIATED DNA REPAIR." OpenSIUC, 2016. https://opensiuc.lib.siu.edu/dissertations/1205.
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Transcriptional elongation is a crucial step in eukaryotic gene regulation whose mis-regulation leads to cellular pathologies. This makes it quite imperative to aim for a better understanding of the processes regulating transcriptional elongation. An important process promoting the association of RNA Polymerase II (RNAPII) with the coding region of the active gene and hence transcriptional elongation is the monoubiquitination of histone H2B at lysine 123. A complex of an E2 conjugase, Rad6p, and an E3 ligase, Bre1p, is essential for this process. Consistent with the role of histone H2B monoubiquitination in promoting the association of RNAPII with the active gene, this process was found to be impaired in the absence of Rad6p or point mutation of lysine 123 to arginine (H2B-K123R). Intriguingly, the association of RNAPII with the coding region of the active gene was not impaired in the absence of Bre1p, even though Bre1p is essential for histone H2B monoubiquitination. However, deletion of Bre1p’s RING domain that is essential for histone H2B monoubiquitination led to an impaired RNAPII association with the active gene. This observation indicates a role of the non-RING domain of Bre1p in repressing the association of RNAPII with the active gene, resulting in no net decrease in RNAPII occupancy in the absence of Bre1p. Taken together, my results implicated both the stimulatory and repressive roles of the histone H2B ubiquitin ligase Bre1p in regulation of RNAPII association with the coding regions of active genes and hence transcriptional elongation. Interestingly, my work also revealed that for efficient transcriptional elongation by histone H2B monoubiquitination, its optimum level needs to be maintained by a proper balance between Rad6p-Bre1p-mediated ubiquitination and de-ubiquitination (DUB) by the DUB module of SAGA. It was found that Sus1p, a subunit of the DUB module, promotes transcriptional elongation, DNA repair and replication via regulation of histone H2B DUB. In addition to Rad6p- Bre1p and the DUB module, global level of histone H2B monoubiquitination is also critically regulated by Cdk9, a kinase essential for phosphorylation of the serine 2 residue in the C-terminal domain (CTD) of RNAPII, which promotes transcriptional elongation. Apart from serine phosphorylation, proline residues at RNAPII-CTD undergo isomerization by proline isomerases, which also regulate transcription. One of the proline isomerases, Rrd1p, has been previously implicated in transcription in response to rapamycin treatment. Based on this fact and Rrd1p’s known interaction with RNAPII-CTD, we predicted that Rrd1p might regulate transcription independently of rapamycin treatment. In agreement with this hypothesis, our work revealed Rrd1p’s role in facilitating transcription of both rapamycin responsive and non-responsive genes in the absence of rapamycin treatment. Consistently, the absence of Rrd1p led to an impaired nucleosomal disassembly at the active gene, which correlates with the role of Rrd1p in promoting transcription. This is because maintenance of proper nucleosomal dynamics is essential for efficient transcription. It is known that transcriptional elongation is facilitated by the regulation of nucleosomal dynamics via the histone chaperone, FACT. Efficient chromatin reassembly in the wake of elongating RNAPII contributing to the fidelity of transcription is promoted by FACT. Being evolutionarily conserved among eukaryotes, FACT is also known to regulate DNA replication and repair, apart from transcription. Intriguingly, FACT has been found to be upregulated in cancers while its downregulation leads to tumor cell death. However, the mechanism which fine-tunes FACT for normal cellular functions remained unknown. My studies revealed a novel mechanism of regulation of FACT by the ubiquitin-proteasome system in yeast. San1p, an E3 ligase involved in nuclear protein quality control, was found to associate with the active gene and regulate transcriptional elongation through its E3 ligase activity- mediated turnover of Spt16p component of FACT. This regulation was found to maintain optimum level of Spt16p/FACT to engage with the active gene for proper transcriptional elongation, DNA repair and replication. In spite of playing such crucial roles in gene regulation, it was not known how FACT is targeted to the active gene. We discovered that a direct physical interaction between FACT and Cet1p, the mRNA capping enzyme, targets FACT to the active gene independently of Cet1p’s mRNA capping activity. Such targeting of FACT to the active gene leads to the release of promoter proximally paused-RNAPII into transcriptional elongation. However, the progress of RNAPII along the active gene during transcriptional elongation is frequently impeded by various kinds of damages along the underlying template DNA. Even though some of these lesions are co-transcriptionally repaired, it was not known whether the repair of extremely toxic DNA double-strand breaks (DSBs) was coupled to transcription. My results showed that DSBs at the transcriptionally active state of a gene are repaired faster than at the inactive state but such repair was not mediated by a co-transcriptional recruitment of DSB repair factors. This observation is in contrast to other DNA repair pathways such as nucleotide excision repair (NER) where repair factors are co-transcriptionally recruited to the lesion containing DNA. In this regard, we found that an NER factor, Rad14p, co-transcriptionally associates with the active gene in the absence of DNA damage to promote transcription, which unraveled a new role of Rad14p in transcription in addition its established role in NER. In summary, my results provide significant novel insights into the regulation of transcriptional elongation and associated processes leading to better understanding of eukaryotic gene expression.
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Lardennois, Alicia. "Contribution of actin cytoskeleton to C. elegans embryonic elongation." Electronic Thesis or Diss., Sorbonne université, 2019. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2019SORUS236.pdf.
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Les processus morphogénétiques impliquent des changements de forme de cellules, via des forces mécaniques, qui doivent être stabilisés. Ma thèse vise à élucider comment l'embryon de C. elegans, matériau élastique, s'allonge progressivement sous l’effet des contractions musculaires. Un crible ARNi en fond pak-1(Ø), kinase de l’épiderme impliquée dans une cascade de mécanotransduction en aval des muscles, a identifié SPC-1/α-spectrine, comme partenaire probable. Les embryons spc-1(-)pak-1(-) s'allongent jusqu'à 1.5-fold, puis reviennent à leur taille initiale sous l’effet des muscles. Avec la microscopie à super-résolution, j’ai montré que leurs faisceaux d'actine épidermiques sont très désorganisés ; suggérant que le remodelage de l'actine pourrait contrer l'élasticité des cellules. Avec un crible en fond spc-1(-)pak-1(-), j'ai identifié deux protéines de fragmentation aidant à rompre les filaments d'actine quand les muscles les courbent fortement. Par ailleurs, la formine de “pontage” FHOD-1 induit aussi une rétraction dans des embryons fhod-1(-);spc-1(-). J'ai surexprimé une construction FHOD-1(ΔFH2/DAD) tronquée en C-terminal qui a partiellement sauvé la rétraction spc-1(-)pak-1(-) suggérant que FHOD-1 bloque la dépolymérisation de l'actine à chaque cycle de contraction. Pour tester cela, j’ai modélisé l'embryon en tant que matériau Kelvin-Voigt soumis à une force épidermique et à la tension musculaire et prédit son allongement en utilisant un composant viscoplastique symbolisant le raccourcissement de l'actine. J'ai donc caractérisé un réseau cellulaire conférant une plasticité mécanique et stabilisant la forme des cellules dans un processus morphogénétiqueBody axis elongation is a fundamental morphogenetic process, involving cell shape changes powered by mechanical forces through small incremental steps which need to be stabilized. During my PhD, I studied C. elegans embryonic elongation to define how the embryo, an elastic material, lengthens progressively upon muscle contractions. Previously, the lab found a kinase, PAK-1, to be mediator of an epidermal mechanotransduction pathway downstream of muscles. Two screens in a pak-1(Ø) background identified α-spectrin SPC-1 as an interactor of PAK-1. spc-1(-)pak-1(-) embryos elongate up to 1.5-fold and then retract to 1-fold in a muscle dependent manner. I used super-resolution microscopy to show that epidermis circumferential actin bundles are highly disorganized in these embryos; suggesting that actin rearrangement could be the lock counteracting elasticity. With a screen in spc-1(-)pak-1(-) background, I identified two severing proteins helping break actin filaments when muscle activity bends them at sharp angles. In addition, the actin bundling formin FHOD-1, was also shown to induce retraction in fhod-1(-);spc-1(-) embryos. I overexpressed a C-terminally truncated FHOD-1(ΔFH2/DAD) that partially rescued the spc-1(-)pak-1(-) retraction suggesting that FHOD-1 blocks further actin depolymerization at each cycle of contraction. To test it, we modeled the embryo as a Kelvin-Voigt material under acto-myosin force from the epidermis and muscle tension. We predicted embryo lengthening using a viscoplastic component accounting for actin shortening. Altogether I characterized a cellular network conferring mechanical plasticity to stabilize cell shape during a morphogenetic process
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Lips, Christian. "Mechanisms of priming and elongation during ubiquitin chain formation." Doctoral thesis, Humboldt-Universität zu Berlin, 2020. http://dx.doi.org/10.18452/20959.
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Die Interaktion von RING-finger-Ubiquitin (Ub)-Ligasen (E3-Enzyme) mit Ub-konjugierenden Enzymen (E2-Enzyme) bestimmt wie schnell ein Zielprotein mit einer Ub-Modifikation versehen wird. In dieser Arbeit wird die Stimulation der E2-Enzyme Ubc6 und Ubc7 durch die E3-Enzyme Hrd1 und Doa10 untersucht. Es wird gezeigt, dass Ubc6~Ub-Konjugate bereitwilliger sogenannte "closed conformations" annehmen als Ubc7~Ub-Konjugate, was wiederum die Tendenz, Ub zu übertragen, steigert. Die katalytische Aktivität von Ubc7 kann durch RING-Domänen stimuliert werden. Durch einen allosterischen Mechanismus, der linchpin allostery, werden Ubc7~Ub-Intermediate in "closed conformations" gedrängt. Zusätzlich werden spezifische Kontakte zwischen RING-finger-Domänen und der Ub-Einheit in einem E2~Ub-Konjugat identifiziert. Diese schränken die Flexibilität des Konjugates weiter ein und begünstigen dadurch die Reaktivität des E2~Ub-Intermediates. Dieser Mechanismus scheint weit verbreitet zu sein und wurde schon bei anderen Ub-Ligasen beobachtet.
Poly-Ub-Signale werden in mehreren Schritten generiert. In einer Priming genannten Reaktion wird die erste Ub-Einheit auf das Zielprotein übertragen. Dieser Vorgang erfordert sehr flexible Enzyme, die in diversem Umfeld Akzeptorstellen finden und mit Ub modifizieren. Die zweite Reaktion, die elongation, umfasst das schrittweise Anheften weiterer Ub-Moleküle an die erste Einheit. Im Gegensatz zum Priming, beruht die Bildung einheitlicher Ketten auf der wiederholten und robusten Konjugation von Ub-Molekülen in gleichbleibendem Milieu. Ub-Ligasen verwenden verschiedene Strategien, um die unterschiedlichen Herausforderungen dieser Reaktionen zu bewältigen. Während Doa10 je ein E2-Enzym pro Reaktion nutzt, kann Hrd1 ein einzelnes E2-Enzym durch linchpin allostery ausreichend stimulieren, um beide Prozesse durchzuführen, wie diese Arbeit zeigt.The interaction of RING-finger ubiquitin (Ub) ligases (E3 enzymes) with Ub conjugating enzymes (E2 enzymes) dictates how fast a Ub modification is synthesized on a client protein. This thesis addresses the catalytic stimulation of the E2 enzymes Ubc6 and Ubc7 by their cognate E3 enzymes Hrd1 and Doa10. Results show that Ubc6~Ub conjugates adopt closed conformations more readily than Ubc7~Ub conjugates, indicative for an inherently higher propensity to transfer Ub. The catalytic activity of Ubc7 can be stimulated by a RING domain which relies on so-called linchpin allostery. This drives Ubc7~Ub intermediates into a closed conformation. In addition, specific contacts of the RING-finger domain and the Ub moiety in an E2~Ub conjugate were identified which further restrict the flexibility of the conjugate and thereby increase the reactivity of the E2~Ub intermediate. This seems to represent a common mechanism for the stimulation of E2 enzymes because similar contacts of RING-finger proteins with Ub have been observed for other Ub ligases. Poly-Ub signals on proteins are generated in successive steps. The first reaction, called "priming", comprises the attachment of an initial Ub moiety to the target. This requires high flexibility of the involved enzymes to modify acceptor sites in a versatile environment. The second step is the sequential addition of Ub to previously attached Ub molecules in a process termed elongation. In contrast to priming, the formation of uniform Ub chains relies on the repeated and robust conjugation of Ub moieties in a mostly invariant setting. Ub ligases employ different strategies to meet the divergent requirements of these reactions. Doa10 uses separate E2 enzymes for priming and elongation. This thesis shows that Hrd1 efficiently stimulates a single E2 enzyme for the catalysis of both steps via linchpin allostery.
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Wang, Mengchi. "Probing the Regulation of Elongation Factor P-Mediated Translation." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1372761617.
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Gocha, April Renee Sandy. "Mechanisms of alternative telomere elongation in human cancer cells." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1351190051.
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Chen, Ying-Hsin. "UNDERSTANDING MECHANISMS THAT COUPLE TRANSLATION ELONGATION AND MRNA DECAY." Case Western Reserve University School of Graduate Studies / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=case1522684403630693.
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Sarala, M. (Marian). "Elongation of Scots pine seedlings under blue light depletion." Doctoral thesis, University of Oulu, 2010. http://urn.fi/urn:isbn:9789514262814.
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Abstract
The elongation response of Scots pine (Pinus sylvestris L.) seedlings to the removal of blue light (400–500 nm) was studied in field experiments in northern Finland. The seedlings were grown in orange or transparent plexiglass chambers or in ambient control plots. The orange plexiglass removed the blue wavelengths from sunlight, while the others served as controls. The experiment was conducted at sub-arctic (69°N) and mid-boreal (64°N) latitudes with three- and two-year-old seedlings originating from 67°N latitude. The response to blue light depletion was also investigated at the 69°N latitude in the following plant subjects: one-year-old Scots pine seedlings of northern (67°N) and southern (62°N) provenances, deciduous Betula pubescens ssp. czerepanovii and Betula pubescens f. rubra seedlings and herbaceous Epilobium angustifolium and Glechoma hederacea plants. Additionally, diurnal change in light quality at the 69°N latitude during the summer was measured.
The elongation of Scots pine seedlings was increased by the removal of blue wavelengths. The increase was more pronounced at the 69°N latitude, while at the 64°N latitude the response was smaller or absent. This is due to increased amount of scattered growth-inhibiting blue light during the nights at the high latitude.
The removal of blue light increased stem elongation in northern origin Scots pine seedlings much more compared to the southern origin seedlings, which suggests that the northern provenance is more sensitive to blue light. Irrespective of that, southern origins also suffer from reduced elongation in the north as they migrate according to climatic change scenarios. However, it is obvious that they grow longer than local origins in the north.
Morphological variables and photosynthetic pigments confirm that the increased elongation of Scots pine seedlings under blue light depletion is not a result of etiolation or it is only a marginal factor. Also, it was neither dependent on temperature nor photosynthesis and growth resources. Instead, the increased elongation is probably a photomorphogenic regulation response of metabolism. In addition, shade intolerant Scots pine, Betula seedlings and herbaceous Epilobium angustifolium responded stronger to blue light removal compared to the more shade-tolerant herbaceous Glechoma hederacea.
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Smith, Abigail J. "Cell biological studies of the transcription elongation factor TFIIS." Thesis, University of Nottingham, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394742.
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Sahoo, Debasis. "Brain injury criteria based on computation of axonal elongation." Thesis, Strasbourg, 2013. http://www.theses.fr/2013STRAD051.
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Ce travail de thèse vise à mieux décrire les mécanismes de lésions de la tête humaine en situation de choc en optimisant le modèle par éléments finis de la tête humaine de Strasbourg (SUFEHM) en termes de modélisation mécanique du crâne et du cerveau grâce à de nouvelles données expérimentales et de techniques récentes d’imagerie médicales. Une première étape a consisté à améliorer la loi de comportement de la boîte crânienne, valider son comportement en regards d’éléments expérimentaux sur cadavres et proposer un MEF capable de reproduire fidèlement la fracture crânienne. La deuxième partie consiste en la prise en compte pour la première fois de l’anisotropie dans les simulations par EF d’accidents réels en utilisant l’Imagerie du Tenseur de Diffusion. Après implémentation, une phase de validation a été entreprise afin de démontrer l’apport de l’anisotropie de la matière cérébrale dans un MEF. Enfin 125 accidents réels ont été reproduits avec le SUFEHM ainsi amélioré. Une étude statistique sur les paramètres mécaniques calculés a permis de proposer des limites de tolérances en termes de fracture crânienne et de lésions neurologiques en s’intéressant tout particulièrement à l’élongation axonale maximale admissible, nouvelle métrique proposéeThe principal objective of this study is to enhance the existing finite element head model. A composite material model for skull, taking into account damage is implemented in the Strasbourg University Finite Element Head Model in order to enhance the existing skull mechanical constitutive law. The skull behavior is validated in terms of fracture patterns and contact forces by reconstructing 15 experimental cases in collaboration with Medical College of Wisconsin. The new skull model is capable of reproducing skull fracture precisely. The composite skull model is validated not only for maximum forces, but also for lateral impact against actual force time curves from PMHS for the first time. This study also proposes the implementation of fractional anisotropy and axonal fiber orientation from Diffusion Tensor Imaging of 12 healthy patients into an existing human FE head model to develop a more realistic brain model with advanced constitutive laws. Further, the brain behavior was validated in terms of brain strain against experimental data. A reasonable agreement was observed between the simulation and experimental data. Results showed the feasibility of integrating axonal direction information into FE analysis and established the context of computation of axonal elongation in case of head trauma. A total 125 reconstructions were done by using the new advanced FEHM and the axonal strain was found to be the pertinent parameter to predict DAI
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Dolch, Lina-Juana. "Glycerolipid metabolism and regulation in Phaeodactylum tricornutum and Nannochloropsis gaditana." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAV026/document.
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Phaeodactylum et Nannochloropsis sont des espèces photosynthétiques modèles pour le métabolisme des glycérolipides, se distinguant par un enrichissement en acides gras polyinsaturés à très longues chaînes (VLC-PUFA) et de grandes quantités en triacylglycérol (TAG). Les proportions des différents lipides sont influencées par des facteurs environnementaux. Nous avons caractérisé le remodelage lipidique chez Phaeodactylum en réponse à la carence en azote et en phosphate. Ces limitations en nutriments induisent une accumulation de TAG, exploitable comme biocarburant. Nous avons identifié de nouveaux composés induisant l'accumulation de TAG et étudié le rôle potentiel du monoxyde d’azote (NO•) dans la régulation du métabolisme lipidique. Nous avons montré qu’en fonction du site de production, le NO• était un signal émis lorsque les conditions de vie étaient critiques, déclenchant l'accumulation de TAG.Les VLC-PUFAs sont produits par des élongases et des désaturases localisées dans le RE. Nous avons identifié une nouvelle classe d’élongases d’acides gras saturés, agissant sur le 16:0, et appelées Δ0-ELO. Le knock out de Δ0-ELO1 de Nannochloropsis réduit le niveau du monogalactosyldiacylglycérol (MGDG), principal lipide des chloroplastes. Ce phénotype met en évidence le rôle de Δ0-ELO1 dans la «voie oméga» qui contrôle le trafic des VLC-PUFAs. Nous avons débuté une dissection de la «voie oméga» par des approches de génétique et des analyses du remodelage lipidique à basse température chez Nannochloropsis. Le diacylglycéryl hydroxyméthyltriméthyl-β-sérine (DGTS) apparaît comme le précurseur de base pour importer des VLC-PUFAs vers le chloroplaste, suivant une voie très régulée du DGTS au MGDG. De plus nous avons montré des fonctions possibles du MGDG et des VLC-PUFAs dans la photoprotection et la régulation de la fluidité membranaire latéralePhaeodactylum and Nannochloropsis are photosynthetic model species for glycerolipid metabolism, standing out by an enrichment of very-long-chain polyunsaturated fatty acids (VLC-PUFAs) and high contents of neutral lipids such as triacylglycerol (TAG). Lipid profiles are influenced by environmental factors. We characterized the lipid remodelling occurring in Phaeodactylum in response to nitrogen and phosphate starvation. Nutrient limitations induce neutral lipid accumulation, which may be exploited as biofuels. We identified new triggers of TAG accumulation and investigated a potential role of nitric oxide (NO•) as second messenger in the regulation of neutral lipid levels. We conclude that in dependence of the production site, NO• serves as a signalling molecule for critical life conditions and thereby triggers TAG accumulation.VLC-PUFAs are produced by ER-located elongases and desaturases. We identified a novel class of elongases, called Δ0-ELOs, acting on saturated fatty acids, most importantly 16:0. Knock out of Δ0-ELO1 in Nannochloropsis resulted in reduced monogalactosyldiacylglycerol (MGDG) levels. MGDG is the major chloroplast lipid. This indicated a role of this initial elongase in fatty acid fate determination and thus in the elusive “omega pathway” for VLC-PUFA trafficking. We have started to investigate the “omega pathway” by reverse genetic approaches and analyses of low-temperature induced lipid remodelling in Nannochloropsis. Diacylglyceryl hydroxymethyltrimethyl-β-serine (DGTS) appears most likely at the base for the chloroplast import of VLC-PUFA, following a dynamically regulated DGTS-to-MGDG pathway. Additionally, we gave insights into possible functions of MGDG and VLC-PUFA in photoprotection and regulation of membrane fluidity
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Többen, Udo. "A novel function for the eukaryotic translation elongation factor 1A." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=972338101.
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Hobson, D. J. "RNA polymerase II collision & its role in transcript elongation." Thesis, University College London (University of London), 2012. http://discovery.ucl.ac.uk/1365987/.
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Antisense non-coding transcripts, genes-within-genes, and convergent gene pairs are prevalent among eukaryotes. The existence of such transcription units raises the question of what happens when RNA polymerase II (RNAPII) molecules collide head-to-head. In this study a combination of biochemical and genetic approaches in yeast are used to show that polymerases transcribing opposite DNA strands cannot bypass each other. RNAPII stops, but does not dissociate upon head-to-head collision in vitro, suggesting that opposing polymerases represent insurmountable obstacles for each other. Head-to-head collision in vivo also results in RNAPII stopping, and removal of collided RNAPII from the DNA template can be achieved via ubiquitylation-directed proteolysis. Indeed, in cells lacking efficient RNAPII poly-ubiquitylation, the half-life of collided polymerases increases, so that they can be detected between convergent genes. These results provide new insight into fundamental mechanisms of gene traffic control, and point to an unexplored effect of antisense transcription on gene regulation via polymerase collision.
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Schwinghammer, Kathrin. "Structure and function of human mitochondrial RNA polymerase elongation complex." Diss., Ludwig-Maximilians-Universität München, 2014. http://nbn-resolving.de/urn:nbn:de:bvb:19-168169.
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Mitochondria are often described as molecular power stations of the cell as they generate most of the energy that drives cellular processes. Mitochondria are eukaryotic organelles with bacterial origin that contain an extra-nuclear source of genetic information. Although most mitochondrial proteins are encoded in the nucleus, the mitochondrial genome still encodes key components of the oxidative phosphorylation machinery that is the major source for cellular adenosine 5’-triphosphate (ATP). The mitochondrial genome is transcribed by a singlesubunit DNA-dependent RNA polymerase (RNAP) that is distantly related to the RNAP of bacteriophage T7. Unlike its T7 homolog, mitochondrial RNA polymerase (mtRNAP) relies on two transcription factors, TFAM and TFB2M, to initiate transcription. The previously solved structure of free mtRNAP has revealed a unique pentatricopeptide repeat (PPR) domain, a
N-terminal domain (NTD) that resembles the promoter-binding domain of T7 RNAP and a C-terminal catalytic domain (CTD) that is highly conserved in T7 RNAP. The CTD adopts the canonical right-hand fold of polymerases of the pol A family, in which its ‘thumb’, ‘palm’ and ‘fingers’ subdomains flank the active center. Since the structure represents an inactive “clenched” conformation with a partially closed active center, only limited functional insights into the mitochondrial transcription cycle have been possible so far.
This work reports the first crystal structure of the functional human mtRNAP elongation complex, determined at 2.65 Å resolution. The structure reveals a 9-base pair DNA-RNA hybrid formed between the DNA template and the RNA transcript and one turn of DNA both upstream and downstream of the hybrid. Comparisons with the distantly related T7 RNAP indicate conserved mechanisms for substrate binding and nucleotide incorporation, but also strong mechanistic differences. Whereas T7 RNAP refolds during the transition from initiation to elongation, mtRNAP adopts an intermediary conformation that is capable of elongation without NTD refolding. The intercalating hairpin that melts DNA during mtRNAP and T7 RNAP initiation additionally promotes separation of RNA from DNA during mtRNAP elongation.
The structure of the mtRNAP elongation complex (this work) and free mtRNAP (previously published) demonstrate that mtRNAP represents an evolutionary intermediate between singlesubunit and multisubunit polymerases. Furthermore, it illustrates the adaption of a phage-like RNAP to a new role in mitochondrial gene expression.
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Belfield, Graham Paul. "The role of elongation factor 3 in yeast protein synthesis." Thesis, University of Kent, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358842.
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Xiong, Yalin. "Downstream NTP effects on human RNA polymerase II transcription elongation." Diss., Connect to online resource - MSU authorized users, 2008.
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Thesis (Ph.D.)--Michigan State University. Dept. of Biochemistry and Molecular Biology, 2008.Title from PDF t.p. (viewed on Apr. 2, 2009) Includes bibliographical references. Also issued in print.