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Literatura académica sobre el tema "Fibre de chromatine"

Autor: Grafiati

Publicado: 4 de junio de 2021

Última modificación: 19 de febrero de 2022

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Artículos de revistas sobre el tema "Fibre de chromatine"

Daban, Joan-Ramon. "The energy components of stacked chromatin layers explain the morphology, dimensions and mechanical properties of metaphase chromosomes". Journal of The Royal Society Interface 11, n.º 92 (6 de marzo de 2014): 20131043. http://dx.doi.org/10.1098/rsif.2013.1043.

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The measurement of the dimensions of metaphase chromosomes in different animal and plant karyotypes prepared in different laboratories indicates that chromatids have a great variety of sizes which are dependent on the amount of DNA that they contain. However, all chromatids are elongated cylinders that have relatively similar shape proportions (length to diameter ratio approx. 13). To explain this geometry, it is considered that chromosomes are self-organizing structures formed by stacked layers of planar chromatin and that the energy of nucleosome–nucleosome interactions between chromatin layers inside the chromatid is approximately 3.6 × 10 −20 J per nucleosome, which is the value reported by other authors for internucleosome interactions in chromatin fibres. Nucleosomes in the periphery of the chromatid are in contact with the medium; they cannot fully interact with bulk chromatin within layers and this generates a surface potential that destabilizes the structure. Chromatids are smooth cylinders because this morphology has a lower surface energy than structures having irregular surfaces. The elongated shape of chromatids can be explained if the destabilizing surface potential is higher in the telomeres (approx. 0.16 mJ m −2 ) than in the lateral surface (approx. 0.012 mJ m −2 ). The results obtained by other authors in experimental studies of chromosome mechanics have been used to test the proposed supramolecular structure. It is demonstrated quantitatively that internucleosome interactions between chromatin layers can justify the work required for elastic chromosome stretching (approx. 0.1 pJ for large chromosomes). The high amount of work (up to approx. 10 pJ) required for large chromosome extensions is probably absorbed by chromatin layers through a mechanism involving nucleosome unwrapping.

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Jack, E. M., C. J. Harrison, G. R. White, C. H. Ockey y T. D. Allen. "Fine-structural aspects of bromodeoxyuridine incorporation in sister chromatid differentiation and replication banding". Journal of Cell Science 94, n.º 2 (1 de octubre de 1989): 287–97. http://dx.doi.org/10.1242/jcs.94.2.287.

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The structure of harlequin-stained chromosomes following substitution with low levels of 5-bromodeoxyuridine (BrdUrd) over two cell cycles and high levels over the last part of one cycle (replication banding) was studied in Chinese hamster ovary (CHO) cells. By using correlative light (LM) and scanning electron microscopy (SEM), it was shown that the effects of both the ultraviolet light (u.v.) and hot SSC treatment steps of the harlequin staining procedure were necessary to obtain sister-chromatid differentiation (SCD) or replication banding. u.v. treatment alone resulted in dark Giemsa staining of both chromatids with SEM morphology of short compact protuberances and an overall flattened smooth appearance in both the unsubstituted and BrdUrd-substituted chromatids, a morphology essentially similar to that of untreated chromosomes. SSC alone on the other hand resulted in dark-staining chromatids with an SEM morphology of raised, loosely packed loops of fibres in both types of chromatids. u.v. and SSC treatment together resulted in differentiation, with dark-staining unifilarly (TB) chromatids in the LM corresponding to raised loosely packed loops in the SEM and pale bifilarly (BB) chromatids corresponding to the smooth compact flattened SEM appearance. Where the BrdUrd-substituted strand became the template (BT), or when the nascent strand TB contained high levels of BrdUrd substitution in replication banding, the chromatid stained pale and showed the compact smooth appearance in the SEM. The Giemsa staining ability and ultrastructural morphology of harlequin staining is discussed with respect to putative DNA loss and also in terms of preferential protein-protein, protein-DNA cross-linkage in BrdUrd-containing DNA. These changes are also compared with the ultrastructural morphology observed after other banding methods, where deterioration of protein and DNA-protein interaction resulting in aggregation of chromatin fibres appears to be the major mechanism.

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Gilbert, Nick y Wendy A. Bickmore. "The relationship between higher-order chromatin structure and transcription". Biochemical Society Symposia 73 (1 de enero de 2006): 59–66. http://dx.doi.org/10.1042/bss0730059.

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It has generally been assumed that transcriptionally active genes are in an ‘open’ chromatin structure and that silent genes have a ‘closed’ chromatin structure. Here we re-assess this axiom in the light of genome-wide studies of chromatin fibre structure. Using a combination of sucrose gradient sedimentation and genomic microarrays of the human genome, we argue that open chromatin fibres originate from regions of high gene density, whether or not those genes are transcriptionally active.

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Barbi, Maria, Julien Mozziconacci, Jean-Marc Victor, Hua Wong y Christophe Lavelle. "On the topology of chromatin fibres". Interface Focus 2, n.º 5 (febrero de 2012): 546–54. http://dx.doi.org/10.1098/rsfs.2011.0101.

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The ability of cells to pack, use and duplicate DNA remains one of the most fascinating questions in biology. To understand DNA organization and dynamics, it is important to consider the physical and topological constraints acting on it. In the eukaryotic cell nucleus, DNA is organized by proteins acting as spools on which DNA can be wrapped. These proteins can subsequently interact and form a structure called the chromatin fibre. Using a simple geometric model, we propose a general method for computing topological properties ( twist , writhe and linking number ) of the DNA embedded in those fibres. The relevance of the method is reviewed through the analysis of magnetic tweezers single molecule experiments that revealed unexpected properties of the chromatin fibre. Possible biological implications of these results are discussed.

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Mullinger, A. M. y R. T. Johnson. "Disassembly of the mammalian metaphase chromosome into its subunits: studies with ultraviolet light and repair synthesis inhibitors". Journal of Cell Science 87, n.º 1 (1 de febrero de 1987): 55–69. http://dx.doi.org/10.1242/jcs.87.1.55.

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Metaphase chromosomes of a simian virus-transformed Indian muntjac cell line have been examined by scanning electron microscopy of material in which the fully packed metaphase structure is progressively relaxed. Such chromosomes are seen in standard, spread preparations of ultraviolet light-irradiated, metaphase-arrested cells, which have been incubated in the presence of inhibitors of DNA synthesis; they are processed for electron microscopy by trypsinization, further fixation and osmium impregnation. Decondensation is initially associated with a gradual elongation and loosening of the chromosome axis and, as loosening proceeds, the appearance of unexpected higher order structures—clusters of 20–40 nm diameter fibres. The arrangement of the clusters shows much variation between spreads. In the most fully extended chromosomes clusters are arranged in two longitudinal series with pairing between sister chromatids; the diameter of the majority of clusters in such chromosomes is in the range 0.4-0.6 micron. In the final stages of decondensation, clusters separate and individual chromosomes are no longer recognizable. Similar fibre clusters are found in interphase nuclei prepared by the same method. We suggest that the clusters of chromatin fibres may assemble as intermediates in the construction of an axial structure, which is further compacted in the fully condensed metaphase chromosome.

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Hashemipour, S. H. "Chromatic Dispersion in Traditional Fiber and Silicon Nanocrystal and Er Doped Fiber Optical Amplifier". International Journal of Engineering and Technology 4, n.º 5 (2012): 518–21. http://dx.doi.org/10.7763/ijet.2012.v4.423.

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Wu, Chenyi y Andrew Travers. "Modelling and DNA topology of compact 2-start and 1-start chromatin fibres". Nucleic Acids Research 47, n.º 18 (20 de junio de 2019): 9902–24. http://dx.doi.org/10.1093/nar/gkz495.

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Abstract We have investigated the structure of the most compact 30-nm chromatin fibres by modelling those with 2-start or 1-start crossed-linker organisations. Using an iterative procedure we obtained possible structural solutions for fibres of the highest possible compaction permitted by physical constraints, including the helical repeat of linker DNA. We find that this procedure predicts a quantized nucleosome repeat length (NRL) and that only fibres with longer NRLs (≥197 bp) can more likely adopt the 1-start organisation. The transition from 2-start to 1-start fibres is consistent with reported differing binding modes of the linker histone. We also calculate that in 1-start fibres the DNA constrains more torsion (as writhe) than 2-start fibres with the same NRL and that the maximum constraint obtained is in accord with previous experimental results. We posit that the coiling of the fibre is driven by overtwisting of linker DNA which, in the most compact forms - for example, in echinoderm sperm and avian erythrocytes - could adopt a helical repeat of ∼10 bp/turn. We argue that in vivo the total twist of linker DNA could be modulated by interaction with other abundant chromatin-associated proteins and by epigenetic modifications of the C-terminal tail of linker histones.

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Racko, Dusan, Fabrizio Benedetti, Dimos Goundaroulis y Andrzej Stasiak. "Chromatin Loop Extrusion and Chromatin Unknotting". Polymers 10, n.º 10 (11 de octubre de 2018): 1126. http://dx.doi.org/10.3390/polym10101126.

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It has been a puzzle how decondensed interphase chromosomes remain essentially unknotted. The natural expectation is that in the presence of type II DNA topoisomerases that permit passages of double-stranded DNA regions through each other, all chromosomes should reach the state of topological equilibrium. The topological equilibrium in highly crowded interphase chromosomes forming chromosome territories would result in formation of highly knotted chromatin fibres. However, Chromosome Conformation Capture (3C) methods revealed that the decay of contact probabilities with the genomic distance in interphase chromosomes is practically the same as in the crumpled globule state that is formed when long polymers condense without formation of any knots. To remove knots from highly crowded chromatin, one would need an active process that should not only provide the energy to move the system from the state of topological equilibrium but also guide topoisomerase-mediated passages in such a way that knots would be efficiently unknotted instead of making the knots even more complex. We perform coarse-grained molecular dynamics simulations of the process of chromatin loop extrusion involving knotted and catenated chromatin fibres to check whether chromatin loop extrusion may be involved in active unknotting of chromatin fibres. Our simulations show that the process of chromatin loop extrusion is ideally suited to actively unknot, decatenate and demix chromatin fibres in interphase chromosomes.

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Heliot, Laurent, Hervé Kaplan, Laurent Lucas, Christophe Klein, Adrien Beorchia, Martine Doco-Fenzy, Monique Menager, Marc Thiry, Marie-Françoise O’Donohue y Dominique Ploton. "Electron Tomography of Metaphase Nucleolar Organizer Regions: Evidence for a Twisted-Loop Organization". Molecular Biology of the Cell 8, n.º 11 (noviembre de 1997): 2199–216. http://dx.doi.org/10.1091/mbc.8.11.2199.

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Metaphase nucleolar organizer regions (NORs), one of four types of chromosome bands, are located on human acrocentric chromosomes. They contain r-chromatin, i.e., ribosomal genes complexed with proteins such as upstream binding factor and RNA polymerase I, which are argyrophilic NOR proteins. Immunocytochemical and cytochemical labelings of these proteins were used to reveal r-chromatin in situ and to investigate its spatial organization within NORs by confocal microscopy and by electron tomography. For each labeling, confocal microscopy revealed small and large double-spotted NORs and crescent-shaped NORs. Their internal three-dimensional (3D) organization was studied by using electron tomography on specifically silver-stained NORs. The 3D reconstructions allow us to conclude that the argyrophilic NOR proteins are grouped as a fiber of 60–80 nm in diameter that constitutes either one part of a turn or two or three turns of a helix within small and large double-spotted NORs, respectively. Within crescent-shaped NORs, virtual slices reveal that the fiber constitutes several longitudinally twisted loops, grouped as two helical 250- to 300-nm coils, each centered on a nonargyrophilic axis of condensed chromatin. We propose a model of the 3D organization of r-chromatin within elongated NORs, in which loops are twisted and bent to constitute one basic chromatid coil.

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Sinclair, Paul, Qian Bian, Matt Plutz, Edith Heard y Andrew S. Belmont. "Dynamic plasticity of large-scale chromatin structure revealed by self-assembly of engineered chromosome regions". Journal of Cell Biology 190, n.º 5 (6 de septiembre de 2010): 761–76. http://dx.doi.org/10.1083/jcb.200912167.

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Interphase chromatin compaction well above the 30-nm fiber is well documented, but the structural motifs underlying this level of chromatin folding remain unknown. Taking a reductionist approach, we analyzed in mouse embryonic stem (ES) cells and ES-derived fibroblasts and erythroblasts the folding of 10–160-megabase pair engineered chromosome regions consisting of tandem repeats of bacterial artificial chromosomes (BACs) containing ∼200 kilobases of mammalian genomic DNA tagged with lac operator (LacO) arrays. Unexpectedly, linear mitotic and interphase chromatid regions formed from noncontiguously folded DNA topologies. Particularly, in ES cells, these model chromosome regions self-organized with distant sequences segregating into functionally distinct, compact domains. Transcriptionally active and histone H3K27me3-modified regions positioned toward the engineered chromosome subterritory exterior, with LacO repeats and the BAC vector backbone localizing within an H3K9me3, HP1-enriched core. Differential compaction of Dhfr and α- and β-globin transgenes was superimposed on dramatic, lineage-specific reorganization of large-scale chromatin folding, demonstrating a surprising plasticity of large-scale chromatin organization.

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Tesis sobre el tema "Fibre de chromatine"

Conde, e. Silva Natalia. "Le nucléosome centromérique et la fibre de chromatine". Paris 6, 2007. http://www.theses.fr/2007PA066131.

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Ce mémoire présente les résultats que j’ai obtenus pendant ces années passées au laboratoire de Biochimie de la Chromatine, le plus souvent en collaboration avec d’autres laboratoires en France, en Ukraine et aux Etats-Unis. Deux questions m’ont particulièrement intéressée : Structure et dynamique du nucléosome centromérique. Le centromère, qui permet la ségrégation des chromatides sœurs pendant la mitose, est un des plus gros complexes nucléaires. Alors qu’on connaît maintenant beaucoup des protéines qui le constituent, on ne savait pratiquement rien sur la structure et la dynamique du nucléosome centromérique, qui a la particularité de contenir un variant de H3 : CENP-A. La technique originale des minicercles, développée au laboratoire depuis de nombreuses années, a été ici irremplaçable. Les résultats, inattendus, nous ont permis de donner un élément de réponse à la question centrale du mécanisme de l’adressage de ce variant d’histone au centromère (article I). Réponse en rotation d’une fibre de chromatine. La réponse en traction d’une fibre de chromatine est relativement bien connue. Mais nous sommes les premiers à avoir étudié sa réponse en rotation, grâce à un système de pinces magnétiques. Les résultats ont permis de généraliser à la fibre de chromatine les notions d’états conformationnels du nucléosome (article II) et de transition chirale du tétrasome (un constituant du nucléosome), initialement mises au jour grâce au système des minicercles. On a ainsi montré que la transition chirale pouvait concerner le nucléosome entier, et pas seulement le tétrasome (article III).

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Garcés, Renata. "Phenomenological theory of chromatin architecture : Liquid-crystalline order induced by nucleosome polarity and chirality correlations". Thesis, Montpellier 2, 2013. http://www.theses.fr/2013MON20132/document.

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Le programme d'expression de gènes dans des cellules eucaryotes dépend fortement de l'état du porteur du génome. L'état physique de la fibre de chromatine est un élément clé de ce programme. Cependant, malgré l'effort considérable fourni pour élucider la structure et les principes physiques de l'organisation de la chromatine, ces principes restent flous. La théorie phénoménologique permet d'analyser l'organisation probable de la chromatine de point de vue thermodynamique. Dans cette thèse, nous étudions l'ordre liquide-cristallin qui résulte de l'équilibre entre le désordre thermique dans la chromatine et les interactions électrostatiques (et mécaniques) de ses constituants. En utilisant les résultats expérimentaux largement acceptés, nous identifions les propriétés robustes mésogènes des nucléosomes (nano-assemblages ADN-protéines) à une petite échelle, et nous montrons comment les corrélations de ces paramètres contrôlent l'ordre qui s'installe dans la chromatine à l'échelle plus grande. Le modèle est basé sur les corrélations des caractéristiques polaires et chirales des nucléosomes. La théorie phénoménologique permet de décrire les phases condensées dans des solutions aqueuses des nucléosomes avec l'ADN linker digéré par des enzymes, aussi bien dans des conditions physiologiques que dans une large gamme de concentration du sel monovalent. Nous utilisons l'hypothèse que pour les mêmes conditions physiologiques les mécanismes physiques qui agissent dans les solutions condensées et dans la fibre sont similaires. Cela nous permet par la suite d'effectuer l'analyse de symétrie, construire le modèle de l'énergie libre, et prédire les états liquide-cristallins hélicoïdaux de la fibre favorisés thermodynamiquement. En plus des modèles de « solénoïde » et de « l'hélice à deux départs » discutés dans la littérature, nous montrons la possibilité des arrangements nucléosomiques « à plusieurs départs » et la biaxialité possible de ces structures. L'effet de l'application d'un champ de force homogène à la fibre de chromatine dans des expériences biochimiques est également étudié. Nous montrons que le déroulement de l'état hélicoïdal est un processus multi-étapes, et nous présentons ses détails structuraux et thermodynamiques
Gene expression program in eukaryotic cells is strongly dependent on physical state of the genome carrier. Physical state of the chromatin is a key element in this program. However, despite the efforts to elucidate the structure and the physical principles underlying the organization of chromatin, they remain largely unknown. Phenomenological theory helps to analyze the most probable chromatin organization. In the present work we study liquid-crystalline order in chromatin resulting from the balance of thermal disorder and electrostatic (and mechanical) interactions of its constituents. Using generally accepted experimental facts we identify robust mesogenic parameters of nucleosomes (DNA-protein nano assemblies) at the smaller scale and show how the correlations of these parameters control the ordering into a chromatin structure at the bigger scale. The model is based on correlation of polar and chiral characteristics of nucleosomes. Phenomenological theory allows us to describe the condensed phases in aqueous solutions of nucleosomes with digested linker DNA, both in physiological conditions and in a wide range of monovalent salt concentration. Using the hypothesis of similar physical mechanism acting in condensed solutions and in the fiber in the same physiological conditions, we perform detailed symmetry analysis, construct the free energy model and reveal the thermodynamically favorable helical liquid-crystalline states of the fiber. In addition to « solenoid » and « two-start-helix » models abundantly discussed previously, we show the possibility of multi-start helix arrangements of nucleosomes in the chromatin and possible biaxiality of the structures. The effects of homogeneous mechanical force field applied to the chromatin in biochemical experiments are also studied. We show that helical state unwinding is a multistep process and we give its structural and thermodynamical details

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Soueidan, Lama. "3D organization of the chromatin fiber". Thesis, Lyon, École normale supérieure, 2015. http://www.theses.fr/2015ENSL0980/document.

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L’état local de la chromatine joue un rôle crucial dans tous les processus génétiques comme le contrôle de la transcription, de la réplication et de la réparation de l’ADN, de la signalisation, etc... La structure précise de l’organisation 3D du deuxième ordre de compaction de la chromatine, aussi appelé fibre de 30 nm, a été le sujet d’intenses débats durant les 40 dernières années. En se basant sur les données in vitro, deux modèles concurrents se distinguent: le solénoïde et le zigzag. Dans le modèle solénoïde, des nucléosomes consécutifs interagissent pour former une trajectoire hélicoïdale avec courbure de l’ADN de liaison. Dans le modèle zigzag, deux hélices d’empilement de nucléosomes se forment, reliées par l’ADN de liaison qui peut être droit ou tordu. Durant ma thèse, j’ai développé une nouvelle approche expérimentale biochimique, appelée ICNN (Identification of the Closest Neighbor Nucleosome), permettant de déchiffrer les interactions entre nucléosomes voisins au sein de la fibre et ainsi de définir sous quelle forme la chromatine se compacte. Nous avons démontré que dans une fibre compactée H1-dépendante, les nucléosomes N+2 sont les plus proches voisins d’un nucléosome N arbitrairement choisit. Ces résultats montrent, sans ambiguïté, l’organisation zigzag de la fibre de 30 nm. De plus, cette organisation reste indépendante de la longueur de l’ADN de liaison, démontrant ainsi que la longueur des nucléosomes (177-227 bp) n’affecte pas la structure de la chromatine et ne peut donc pas être responsable de l’hétérogénéité structurale décrite dans la littérature. La dynamique et la structure de la chromatine peuvent être affectées par l’incorporation de variants d’histones. Nos expériences utilisant des assemblages H2A.Z ne montrent aucune différence de repliement entre les fibres contenant H2A.Z et H2A. Ces données suggèrent que le mécanisme de régulation de la transcription spécifique de H2A.Z est indépendant du repliement de la chromatine. CENP-A est un élément de la chromatine centromérique indispensable à la division cellulaire. Les images cristallographiques montrent que les nucléosomes contenant CENP-A sont plus ouverts que le nucléosomes conventionnels à cause d’une hélice α-NCENP-A plus courte. Parallèlement, des résultats récents de notre laboratoire ont montré que H1 ne se lie pas d’une façon stable aux nucléosomes contenant CENP-A, ne conduisant à aucune organisation de l’ADN de liaison (données non publiées). Notre étude au niveau de la chromatine a confirmé l'absence de repliement de la fibre contenant CENP-A en présence de H1. De manière intéressante, le remplacement de CENP-A par un mutant α-NH3-CENP-A restaure la bonne liaison de H1 et le repliement de la fibre avec une conformation habituelle en zigzag comme dans une fibre contenant H3
The local chromatin state plays a crucial role in all fundamental DNA-templated processes, such as transcription control, DNA replication or repair, signaling, etc. The precise 3D organization of the second level folding, the so-called 30 nm fiber, has been a matter of intense speculations and debates over the past 40 years. Two competing models have been proposed on the basis of in vitro data, the solenoid and zigzag arrangements. In the solenoid model, consecutive nucleosomes interact with each other and follow a helical trajectory with bent DNA linker. In the zigzag model, alternate nucleosomes interact with each other with straight, twisted or coiled linker DNA. During my thesis, I developed a new biochemical approach, called ICNN (Identification of the Closest Neighbor Nucleosomes), allowing a direct “visualization” of the neighboring nucleosomes within H1-dependent compacted chromatin. We showed that within H1-compacted regular nucleosomal array, N±2 nucleosomes are the nearest neighboring interaction partners of any arbitrary nucleosome N. This finding provides an unambiguous evidence for the zigzag two-start helix conformation of the 30 nm fiber. Furthermore, this organization remains independent on the DNA linker length, demonstrating that the nucleosome repeat length (177-227 bp) does not affect the chromatin structure and therefore cannot be a reason for chromatin structural heterogeneity as suggested in the literature. Chromatin structure and dynamics might be affected by the incorporation of histone variants. Our ICNN experiments with H2A.Z arrays showed no difference of folding between H2A.Z- and H2A-containing fibers. This finding suggests that the H2A.Z-specific transcriptional regulation involves mechanisms other than chromatin folding. CENP-A is a hallmark for centromeric chromatin that is indispensable for cell division. X-ray scattering in crystals showed that CENP-A-containing nucleosomes are more “open” than conventional ones due to the shorter α-NCENP-A helix. Besides, recent results in our lab showed that H1 does not stably bind to the CENP-A nucleosomes and that no stem organization of the linker is formed (not published). Our ICNN study at the chromatin level confirmed the absence of H1-induced folding of a regular CENP-A array. Interestingly, replacement of CENP-A with the α-NH3-CENP-A mutant restored proper H1 binding and folding of the fiber into the usual zigzag conformation, as does the conventional H3-containing fiber

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Bancaud, Aurélien. "Dynamique et structure de fibres de chromatine individuelles". Paris 6, 2004. http://www.theses.fr/2004PA066432.

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Robinson, Philip Jeremy John. "Reconstitution, folding and structure of the '30nm' chromatin fibre". Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615297.

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Gilbert, Nick. "Nature and modulation of the higher-order chromatin fibre". Thesis, University of Edinburgh, 2000. http://hdl.handle.net/1842/28098.

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In this project I have analysed and modulated the higher-order chromatin fibre to determine the role this fibre plays in the regulation of cellular processes. By analysing the chromatin fibre from cells with different differentiation potentials I have been unable to show that there are any inherent differences between the chromatin fibres and that the conformation of the chromatin fibre does not alter when these cells are differentiated. Interestingly, I have found that the chromatin fibres do have inherent differences in their nuclease sensitivities, suggesting that although the overall structures are similar there are some differences between cells with various differentiation potentials. To establish whether an alteration in the chromatin conformation will alter a cell's differentiation potential I have expressed histone H5, a replacement linker histone normally found in nucleated erythrocytes, in pluripotential embryonic stem (ES) cells. My results showed that constitutive expression of H5 in ES cells causes substantial cell death and although I have a regulated, tetracycline based, histone H5 expression construct I was unable to express H5 in a controlled manner to investigate the underlying chromatin structure. In addition, I expressed mutant H5 molecules in ES cells which also caused substantial cell death, so in conclusion I was unable to determine whether this cellular phenotype was directly due to an alteration in chromatin structure or a non-specific effect from expressing a positively charged molecule in ES cells. As a first step towards studying the expression of linker histones in living cells and during development, I constructed and analysed a green fluorescent protein (GFP)-histone H5 fusion. As for histone H5, the GFP-H5 fusion protein is correctly expressed in a variety of cell types, but is lethal to cells when expressed at high levels for longer periods of time.

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Huynh, V. "Reconstitution of the 30-nm chromatin fiber". Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604906.

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This thesis describes the production of folded and regular 30-nm chromatin fibers reconstituted from purified components of DNA tandem repeats, histone octamer, and H5. Obtaining evenly spaced nucleosome arrays saturated with H5 is feasible with the use an artificially derived sequence with a high affinity for histone octamer. This artificial "sequence 601" positions the nucleosome specifically and uniquely. Folding of the 30-nm chromatin fiber requires that each DNA repeat (200 bp) be found or saturated with exactly one histone octamer and one H5. The basis of the reconstitution system presented in this thesis is the addition of mixed sequence competitor (or carrier) DNA which allows the reconstitution to be fully controlled. A combination of techniques including bandshift assays, restriction enzyme digestion, and electron microscopy are used to analyze the regularity and fully saturated nature of the reconstituted chromatin. The reconstituted chromatin arrays are shown to fold to form compact 30-nm chromatin particles as visualized by electron microscopy. The results suggest that a DNA fragment containing at least 19 tandem 200 bp 601 repeats (200-19mer) is required to produce stably folded particles as 200-12mer DNA repeats did not show sufficient stability. Analysis by cryoelectron microscopy showed that the reconstitution of 200-19mer DNA repeats resulted in both single chromatin particles and oligomerized chromatin fibers. Furthermore, the reconstituted chromatin fibers have a morphology similar to that of native chromatin fibers with the exception of appearing to be more regular (as desired). The production of regular chromatin fibers is a critical step towards the structural determination of the 30-nm chromatin fiber. Furthermore, these folded and reconstituted chromatin fibers provide the ideal substrate to address future questions of the role of higher order chromatin structure in biological processes.

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Carrivain, Pascal. "Des moteurs de jeux à la physique des chromosomes". Phd thesis, Université Pierre et Marie Curie - Paris VI, 2012. http://tel.archives-ouvertes.fr/tel-00802204.

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Durant ces dernières années, la modélisation en physique est restée aveugle aux développements de disciplines sœurs ; en particulier la mécanique ou plutôt la robotique qui développe des outils puissants comme la cinématique inverse et les moteurs physiques (ou moteurs de jeux). Ces techniques sont couramment employées dans les jeux vidéo pour des résultats très réalistes. Je propose ici de montrer que nous pouvons simuler des assemblages d'ADN et de protéines (fibre de chromatine et à plus grande échelle des chromosomes) comme des systèmes articulés avec un moteur physique. Je montre aussi qu'il est possible d'étendre le thermostat local de Langevin à un thermostat global pour accélérer l'échantillonnage de l'espace des configurations du système ADN-protéines dans l'ensemble canonique. Ce nouveau thermostat est particulièrement intéressant lorsqu'il est utilisé avec un moteur physique. Plus précisément, je montrerai que la simulation que j'ai développée reproduit les résultats expérimentaux de manipulation de molécules uniques sous pinces magnétiques et permet de faire des prédictions. Enfin, cette simulation offre des perspectives intéressantes pour la modélisation des noyaux d'organismes allant de la drosophile à l'humain et la compréhension des toutes dernières données sur l'architecture des génomes.

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Vergnole, Sébastien. "Nouveaux interféromètres large bande pour l'imagerie haute résolution : interféromètre fibré hectométrique : utilisation des Fibres à Cristaux Photoniques". Limoges, 2005. http://aurore.unilim.fr/theses/nxfile/default/b5576baa-1781-4524-9024-362d7aa12695/blobholder:0/2005LIMO0022.pdf.

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L'imagerie haute résolution a atteint une grande maturité ces dernières années et donne lieu aujourd'hui à de nombreuses publications scientifiques. Deux techniques sont utilisées : l'optique adaptative et la synthèse d'ouverture. Cette dernière technique est au point pour des bases de l'ordre de la centaine de mètres. Mais de nouvelles avancées sont encore possibles notamment en se tournant vers des instruments à très grandes bases et/ou utilisant de nouveaux guides optiques. Par ailleurs, le domaine de l'astronomie imposant de travailler avec de larges bandes spectrales pour collecter plus de lumière, la mise au point d'interféromètres large bande se révèle indispensable. Ce manuscrit présente le développement d'instruments fibrés et leur caractérisation sur de larges domaines spectraux. Après une première partie consacrée à quelques rappels théoriques, le deuxième volet de ce document est consacré à l'étude des fibres optiques en silice pour le projet `OHANA. Ce projet, piloté par l'Observatoire de Meudon, vise à relier de manière cohérente les télescopes du Mauna Kea à Hawaii à l'aide des fibres optiques. La dispersion chromatique différentielle des fibres destinées à relier le CFHT et Gemini, d'une longueur de 300 m, a été caractérisée ce qui a permis de la minimiser. Une étude de l'évolution de cette dispersion a également été menée en tenant compte des variations différentielles de température. Des solutions utilisant une ligne à retard fibrée ou des lames de CaF2 ont été proposées et réalisées pour compenser la dispersion supplémentaire occasionnée par ces variations des contraintes thermiques. La troisième partie est dédiée à l'étude des propriétés des fibres à cristaux photoniques (PCFs) pour l'interférométrie large bande. Deux interféromètres respectivement à deux et trois voies ont été mis en oeuvre dans le but de tester les propriétés des PCFs. Il a été montré que les fibres microstructurées utilisées avaient la capacité de propager la lumière de façon cohérente sur une très large bande spectrale, allant typiquement de 670 nm et 1550 nm, ce qui n'est pas possible en utilisant des fibres en silice "conventionnelles". Enfin, des mesures de clôture de phase ont été réalisées et font apparaître que ces PCFs n'apportent pas de biais sur ces mesures
High resolution imaging has reached a high reliability and currently gives a lot of scientific results. Nowadays, we may develop this technique by using very long baselines and/or new optical waveguides. Moreover, astronomers are working with wide band spectra to get more light. Thus, the study of wide band interferometers is essential. This manuscript reports the development and the characterization of wide band fiber interferometers. The first part deals with some theoretical notions. The second part is dedicated to the study of silica optical fibers in the frame of the `OHANA project. The aim of this project driven by Paris Observatory is to coherently link the telescopes of the Mauna Kea in Hawaii thanks to optical fibers. The differential chromatic dispersion of the 300-m long fibers dedicated to link CFHT and Gemini telescopes has been characterized and minimized. The effect of the temperature variation has been also studied. Solutions using an optical fiber delay line or CaF2 glasses plates have been proposed and implemented to compensate the additional chromatic dispersion due to temperature effects. The last part of this manuscript is devoted to the study of Photonic Crystal Fibers (PCFs) for wide band interferometry. A two-beam and a three-beam interferometers have been implemented to test the properties of PCFs. It has been shown that the microstructured fibers used in our experiment are able to coherently propagate light over a wide spectral domain from 670 nm to 1550 nm. This wide domain is impossible to reach with "conventional" fibers. At last, closure phase measurements have been carried out showing that these PCFs do not bring additional defects on these measurements

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Vergnole, Sébastien. "Nouveaux interféromètres large bande pour l'imageriehaute résolution : interféromètre fibré hectométrique ;utilisation des Fibres à Cristaux Photoniques". Phd thesis, Université de Limoges, 2005. http://tel.archives-ouvertes.fr/tel-00012003.

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Libros sobre el tema "Fibre de chromatine"

Leuba, Sanford H. On the location of the linker histones and the linker DNA in the 30 nm fiber of chromatin. 1993.

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Guenther, B. D. Modern Optics Simplified. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780198842859.001.0001.

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This textbook is designed for use in a standard physics course on optics at the sophomore level. The book is an attempt to reduce the complexity of coverage found in Modem Optics to allow a student with only elementary calculus to learn the principles of optics and the modern Fourier theory of diffraction and imaging. Examples based on real optics engineering problems are contained in each chapter. Topics covered include aberrations with experimental examples, correction of chromatic aberration, explanation of coherence and the use of interference theory to design an antireflection coating, Fourier transform optics and its application to diffraction and imaging, use of gaussian wave theory, and fiber optics will make the text of interest as a textbook in Electrical and bioengineering as well as Physics. Students who take this course should have completed an introductory physics course and math courses through calculus Need for experience with differential equations is avoided and extensive use of vector theory is avoided by using a one dimensional theory of optics as often as possible. Maxwell’s equations are introduced to determine the properties of a light wave and the boundary conditions are introduced to characterize reflection and refraction. Most discussion is limited to reflection. The book provides an introduction to Fourier transforms. Many pictures, figures, diagrams are used to provide readers a good physical insight of Optics. There are some more difficult topics that could be skipped and they are indicated by boundaries in the text.

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Capítulos de libros sobre el tema "Fibre de chromatine"

Mitschke, Fedor. "Chromatic Dispersion". En Fiber Optics, 55–85. Berlin, Heidelberg: Springer Berlin Heidelberg, 2016. http://dx.doi.org/10.1007/978-3-662-52764-1_4.

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Mitschke, Fedor. "Chromatic Dispersion". En Fiber Optics, 47–74. Berlin, Heidelberg: Springer Berlin Heidelberg, 2009. http://dx.doi.org/10.1007/978-3-642-03703-0_4.

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Carretero, M. I., C. C. Arraztoa, C. I. Casaretto, W. Huanca, D. M. Neild y M. S. Giuliano. "Alpaca sperm chromatin evaluation using Toluidine Blue". En Fibre production in South American camelids and other fibre animals, 141–44. Wageningen: Wageningen Academic Publishers, 2011. http://dx.doi.org/10.3920/978-90-8686-727-1_18.

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Walling, Jason G. y Jiming Jiang. "DNA and Chromatin Fiber-Based Plant Cytogenetics". En Plant Cytogenetics, 121–30. New York, NY: Springer New York, 2011. http://dx.doi.org/10.1007/978-0-387-70869-0_5.

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Tiana, Guido y Luca Giorgetti. "Coarse Graining of a Giant Molecular System: The Chromatin Fiber". En Methods in Molecular Biology, 399–411. New York, NY: Springer New York, 2019. http://dx.doi.org/10.1007/978-1-4939-9608-7_17.

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Amiri, Iraj Sadegh y Masih Ghasemi. "Device Characterizations and Chromatic Dispersion Measurement in Optical Fibres". En SpringerBriefs in Electrical and Computer Engineering, 41–66. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-10585-3_5.

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Travers, Andrew. "Paradox Regained: a Topological Coupling of Nuclesomal DNA Wrapping and Chromatin Fibre Coiling". En Mathematics of DNA Structure, Function and Interactions, 321–29. New York, NY: Springer New York, 2009. http://dx.doi.org/10.1007/978-1-4419-0670-0_15.

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Zuo, Chun-Cheng, Yong-Wu Zhao, Yong-Xia Zuo, Feng Ji y Hao Zheng. "Computer Simulation on the Compaction of Chromatin Fiber Induced by Salt". En Lecture Notes in Computer Science, 413–20. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-15615-1_49.

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Elcock, Lauren S. y Joanna M. Bridger. "Fluorescence In Situ Hybridization on DNA Halo Preparations and Extended Chromatin Fibres". En Methods in Molecular Biology, 21–31. Totowa, NJ: Humana Press, 2010. http://dx.doi.org/10.1007/978-1-60761-789-1_2.

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Tawade, Laxman, Shantanu Jagdale, Munir Sayyad y Sanjay Nalbalwar. "A Novel Analysis of Single Mode Fiber for Reduction of Chromatic Dispersion Using Dispersion Compensated Fiber". En Advanced Communication and Networking, 124–33. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-13405-0_13.

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Actas de conferencias sobre el tema "Fibre de chromatine"

Bernard, J. J. y J. Guillon. "Bandwidth Enhancement By Correcting Chromatic Dispersion Of 1.55µm Single-Mode Fibre Links". En Fibre Opitcs '86, editado por Lionel R. Baker. SPIE, 1986. http://dx.doi.org/10.1117/12.963596.

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Hauske, F. N., C. Xie, Z. Zhang, C. Li, L. Li y Q. Xiong. "Frequency Domain Chromatic Dispersion Estimation". En National Fiber Optic Engineers Conference. Washington, D.C.: OSA, 2010. http://dx.doi.org/10.1364/nfoec.2010.jtha11.

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Li, Z. L., L. S. Yan, L. Y. Shao, W. Pan y B. Luo. "Coherent BOTDA Sensor with Suppressed Chromatic Dispersion". En Optical Fiber Communication Conference. Washington, D.C.: OSA, 2015. http://dx.doi.org/10.1364/ofc.2015.w3i.4.

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Pillai, Bipin Sankar Gopalakrishna, Behnam Sedighi, William Shieh y Rodney S. Tucker. "Chromatic Dispersion Compensation - An Energy Consumption Perspective". En Optical Fiber Communication Conference. Washington, D.C.: OSA, 2012. http://dx.doi.org/10.1364/ofc.2012.om3a.8.

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Benlachtar, Y., R. I. Killey y P. Bayvel. "Chromatic dispersion monitoring using synchronous sampling". En OFCNFOEC 2006. 2006 Optical Fiber Communication Conference and the National Fiber Optic Engineers Conference. IEEE, 2006. http://dx.doi.org/10.1109/ofc.2006.215584.

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Chatterjee, Souvik y Takashi Nakajima. "Resonant Auger Electron dynamics in bi-chromatic Laser field". En International Conference on Fibre Optics and Photonics. Washington, D.C.: OSA, 2016. http://dx.doi.org/10.1364/photonics.2016.th4f.1.

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ELREFAIE, A. F., R. E. WAGNER y D. A. ATLAS. "Chromatic dispersion limitations in coherent lightwave transmission systems". En Optical Fiber Communication Conference. Washington, D.C.: OSA, 1988. http://dx.doi.org/10.1364/ofc.1988.wq42.

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Delevaque, E. "Chromatic dispersion compensation using Bragg grating photoinduced within accurately tapered fibres". En IEE Colloquium on Optical Fibre Gratings. IEE, 1997. http://dx.doi.org/10.1049/ic:19970251.

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Fortenberry, R. M., M. A. Scobey, D. J. Derickson, L. F. Stokes y P. C. Egerton. "Chromatic dispersion of thin film filters". En 2005 Optical Fiber Communications Conference Technical Digest. IEEE, 2005. http://dx.doi.org/10.1109/ofc.2005.193142.

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Martins, C. S., S. B. Amado, S. M. Rossi, A. Chiuchiarelli, J. D. Reis, A. Carena, F. P. Guiomar y A. N. Pinto. "Low-Complexity Chromatic Dispersion Equalizer for 400G Transmission Systems". En Optical Fiber Communication Conference. Washington, D.C.: OSA, 2017. http://dx.doi.org/10.1364/ofc.2017.th2a.56.

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Informes sobre el tema "Fibre de chromatine"

McKinney, Jason D. y John Diehl. Measurement of Chromatic Dispersion using the Baseband Radio-Frequency Response of a Phase-Modulated Analog Optical Link Employing a Reference Fiber. Fort Belvoir, VA: Defense Technical Information Center, septiembre de 2007. http://dx.doi.org/10.21236/ada472284.

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