Дисертації з теми "P9"

The IncIl conjugative plasmid ColIb-P9 carries a psiB gene that prevents induction of the SOS response in host bacteria. This locus was found to be located 2.5 kb downstream of the ssb (single-stranded DNA- binding protein) gene in the leading region of ColIb. This portion of the plasmid is transferred first to the recipient cell during conjugation and is strikingly similar to part of the leading region of the otherwise distinct F plasmid. Determination of the nucleotide sequence of ColIb psiB demonstrated that the gene has 84% identity with the psiB gene of F. Promoterless lacZ fusions on ColIb were created to leading region genes ssb and psiB and to sog, a representative transfer gene. It was found that expression of all three genes is increased when the ColIb transfer system is derepressed, but ssb and psiB are expressed at a much lower level than sog. Expression of psiB and ssb is increased when the host cell is exposed to UV- irradiation or mitomycin C treatments. The DNA-damage inducibility of ssb and psiB is recA and lexA-independent showing that neither gene is a component of the SOS regulon. Expression of both psiB and ssb is strongly enhanced in conjugatively infected recipient cells. No enhanced synthesis of Sog polypeptides was detected following conjugation showing that the zygotic induction of ssb and psiB is not a general property of plasmid genes. The implication is that PsiB and SSB proteins function in the transconjugant cell, rather than in the primary donor. It has been proposed that PsiB acts to prevent triggering of the SOS response during conjugation by transferring single-stranded DNA. Consistent with this hypothesis, carriage of the psiB gene by ColIb was shown to prevent a low level of SOS induction following conjugation. Plasmids that carry ssb and psiB genes have replicons belonging to the RepFIC family. It is postulated that the trigger for SOS induction during conjugation may be generated during the initial replication of the plasmid in the newly infected recipient cell rather than by the process of single-stranded DNA transfer.

This thesis concerns the cortical connectivity in Primates. The efficacy of Diffusion weighted MRI (dMRI) is examined. White matter (“WM”) systems subjacent to cortex (“superficial WM” ) are found to be a limiting factor to dMRI tractography. Superficial WM systems are examined with dMRI itself, and with analysis of histological data from the scanned brains. dMRI data was acquired ex-vivo at exceptional spatial and angular resolution (250μm in Rhesus, 150μm in Marmoset). The superficial WM was found to be complex, and with current dMRI methods, an effective barrier to tracking to and from around 50% of cortex in Rhesus. The quality of our data allowed Gray matter seeding, so that penetration both into and out of cortex was examined. We summarize the history of cortical connectivity and current work in tractography. We present an account of the formation and properties of the superficial WM. We compare tracking behaviors to tracer results, and develop a series of scalar maps on cortical surface models to summarize tracking behaviors. We attempt to explain these maps by examining the underlying tracking behavior and the brain tissue itself, revealing the intricate nature of the superficial WM. Chapter 4 contains a separate but related project in which a histologically accurate high resolution 3D and surface atlas of the Rhesus cortex is constructed with unprecedented accuracy. A method to rapidly and accurately non-linearly transform the atlas to a scan of another animal is developed, thus labelling its cortex. accuracy is by comparison to histology of the scanned animals.

Understanding the impacts of landscape fragmentation, degradation and hunting on arboreal species of conservation concern, such as the critically endangered brownheaded spider monkey (Ateles fusciceps fusciceps), remains a major challenge in conservation biology. Current research on the population status of this primate and the area it inhabits in the Ecuadorian Choco is urgently needed to aid in the design of specific and effective conservation strategies. I surveyed the population of A. f. fusciceps in the unprotected forest cooperative Tesoro Escondido in the buffer zone of the Cotacachi Cayapas Ecological Reserve during the year 2012-2013. Using the line transect method I estimated a population density of 15.79 individuals/km2. I found an average subgroup size of 3.42 individuals and a female biased population. Identifying key food resources for critically endangered species is vital in their conservation, particularly if these resources are also targeted by anthropogenic activities such as logging. The province where A. f. fusciceps is found is also heavily dependent on commercial logging with no information available on its impacts on key feeding resources for this primate. I characterised the oristic composition of the habitat of A. f. fusciceps and estimated the availability of fruit resources for the annual cycle of 2012-2013 in sixteen 0.1 hectare vegetation plots. I determined feeding preferences for A. f. fusciceps using behavioural observations applying the Chesson ε index to identify key feeding tree species. I reviewed regional logging permits to identify species targeted for extraction by the timber industry and calculated extraction volumes in primary forest for key feeding tree species to identify potential conflict between logging and primate diet. I identified 65 fruiting tree species from 34 families that formed the diet of A. f. fusciceps . The Chesson ε index identified twelve species as preferred species with further phenological observations identifying seven species as staple foods and two palms as potential foods consumed in times of fruit scarcity. Additionally, I found that the lipid rich fruits of Brosimum utile make this an important resource for this primate throughout the year. Furthermore, of 65 feeding tree species identified for A. f. fusciceps , 35 species are also targeted as sources of timber. Five key feeding species would be depleted under current sustainable management extraction protocols while two other species would be significantly impacted in terms of local abundance. Hunting pressure on A. f. fusciceps has been reported as one of the main causes of its population decline. However, no current research on the extent of this activity or its causes was available. I carried out semi-structured interviews in nine indigenous Chachi villages, as well as two Colono towns, to evaluate the occurrence of hunting activity and to identify drivers, attitudes and behaviour of hunters. In total I interviewed 62 people, 41 Chachis and 21 Colonos. From the Chachi interviewees 93% identified themselves as hunters, with subsistence hunting the main driver for this activity and central to their culture, especially for men. Colonos identified less with this activity (only 38%), and with more varied reasons, such as commerce and conflict. Only Chachis accepted the hunting of spider monkeys, with the main reason given as their taste. Keeping spider monkeys as pets was also a regular activity prior to tougher law enforcement by the Ministry of Environment (MAE). Information on medicinal uses from spider monkeys was also gathered, as well as information of other species hunted in the area. Even though Ecuadorian law recognises the right of indigenous peoples to hunt within their territories, it also forbids hunting critically endangered species. From the interviews it is evident that information and understanding of this law has not been successfully transmitted. Determining the effects of fragmentation, hunting and habitat degradation on populations viability of this primate is crucial before investing heavily in local sustainable livelihoods and conservation initiatives. A range of fragmentation metrics are available to study habitat fragmentation, yet their relationship to survival of populations of conservation concern remains to be quantified. I applied an agent-based model (ABM), calibrated on field-collected datasets on forest fruit dynamics, behaviour and feeding ecology of A. f. fusciceps, to first identify an optimised fragmentation statistic to be used to screen satellite imagery and identify remaining priority conservation areas in unprotected, fragmented forests in NW Ecuador. I then used the ABM to further explore the combined impacts of fragmentation, hunting and logging. Mean Patch Area was the best fragmentation metric predictor of population numbers, I identified a MPA of 174.9 hectares as the cut-off point for the survival of brown-headed spider monkeys given the lowest combinations of logging activity and hunting pressure and I used it to identify priority conservation areas in NW Ecuador. Implementing conservation strategies in areas where people and nature interact is a challenging task. I designed a step by step framework for the conservation of critically endangered species. Based on my experience with Ateles fusciceps fusciceps as a case study, I present the design, assessment and implementation of different community-based strategies.

The psiB and ssb genes of IncI1 plasmid ColIb-P9 reside in the leading region, which is the first portion of the plasmid to be transferred during conjugation. These genes are expressed in a transient burst in newly-formed transconjugants via a process known as zygotic induction, and are thought to promote establishment of the immigrant plasmid. One hypothesis for the regulation of zygotic induction is that the genes are activated as part of a conjugation-induced heat-shock response. Both ssb and psiB are damage-inducible and have putative sigma 32-dependent promoter sequences. Data are presented showing that zygotic induction occurs when sigma 32 levels are limited and that conjugation fails to induce the heat- shock response, as measured using a sigma 32-dependent reporter construct. A second hypothesis is that zygotic induction results from a transient loss of negative supercoiling during plasmid transfer. The finding that neither psiB nor ssb expression is strongly induced in vegetative cells treated with coumermycin is inconsistent with this hypothesis. A third possibility is that psiB and ssb are regulated by a plasmid-encoded trans-acting repressor which is absent from the recipient cell. This hypothesis was tested with an entry-exclusion mutant of ColIb, created by insertional inactivation of the eex locus. When ColIb was transferred to a recipient harbouring this mutant, zygotic induction was observed. This finding also demonstrates that zygotic induction is independent of vegetative replication, since the incoming and resident plasmids are incompatible. Previous work suggested that psiB and ssb are closely linked to promoters. However, data obtained using RP4- and ColIb-mobilisable constructs carrying different portions of the leading region suggest that at least 5 kb of upstream DNA is necessary for zygotic induction of both genes, thus indicating that they are induced as part of a leading region operon.

Conjugative transmission of enterobacterial plasmid ColIb was found to be relatively resistant to type I and type II restriction systems specified by the recipient cell. One process contributing to evasion of restriction barriers during conjugation apparently involves transfer of multiple copies of the plasmid. A more specialized anti-restriction mechanism requires the product of the ColIb ard (alleviation of restriction of DNA) gene. The Ard phenotype was discovered from the ability of ColIb to alleviate EcoK (type I) restriction of unmodified infecting the plasmid-harbouring cell. Ard activity alleviated restriction of phage by representatives of all three families of type I R-M system, but not by type II or type in systems. ColIb had no effect on the modification activity of EcoK but this activity was impaired by multicopy recombinant plasmids supporting overexpression of ard. A 498 nucleotide sequence corresponding to ard was identified. The Ard protein (apparent mass of c22 KDa) was visualised following in vitro transcription and translation of ard+ recombinant plasmids. Gene fusion studies indicated that only the C-terminal two-thirds of the Ard protein is necessary for the restriction alleviation phenotype. A ColIbdrd ard mutant was constructed by a gene replacement strategy. Properties of the plasmid showed that Ard protects ColIb from EcoK restriction following conjugative transfer and that protection requires expression of the gene on the immigrant plasmid. The ard gene is located in the leading region, which is the portion of ColIb transferred first in conjugation, and is near to the psiB and ssb loci. The latter two genes are known to be zygotically induced following transfer. However, studies with lacZ reporter probes showed that ard was not subject to zygotic induction; the gene is apparently expressed at very low levels before, and after conjugative transfer. It is proposed that ard facilitates the productive transfer of ColIb between its different natural enterobacterial hosts.

The Incil plasmid Colib-P9 was found to carry a single-stranded DNA-binding protein gene (ssb), and the cloned gene was able to suppress the UV and temperature-sensitivity of an ssb-l strain of Escherichia coli K-12. Determination of the nucleotide sequence of Colib ssb demonstrated that the gene shows considerable homology to the ssb gene of plasmid F. In contrast, Southern hybridization techniques indicated that the IncP plasmid RP4 lacks a gene with any extensive homology to F ssb. It was shown that the direction of transfer of Colib-P9 is such that the Colib ssb gene, which lies approximately 11 kb from the origin of transfer, is located within the region transferred early during conjugation. The Colib and F ssb genes are therefore similarly located on their respective plasmids. The Colib ssb gene was shown to be coordinately expressed with the transfer (tra) genes, suggesting that the Colib SSB protein may participate in the conjugative process. However, a mutant Colibdrd-1 derivative carrying a Tn903-derived insertion in ssb showed no defect in tests of conjugative efficiency and was apparently maintained stably both following mating and during vegetative growth. Thus no biological role for the Colib SSB protein was detected. However, unlike the parental plasmid, the Colib ssb mutants conferred a marked Psi- (plasmid- mediated SOS inhibition) phenotype on recA441 and recA730 strains. This may result from high level expression of a psi gene due to readthrough from the Tn903 insertion. It is now apparent that many conjugative plasmids previously thought to be unrelated may be derived from a common ancestral plasmid which possessed both ssb and psi genes. It is speculated that the function of the SSB proteins of conjugative plasmids such as Colib and F may subsequently have been duplicated by analogues derived from newly aquired conjugation systems.

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Ciência e Engenharia de Materiais.
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O presente trabalho investigou a viabilidade do uso da técnica da dupla-camada, visando estabelecer adequados procedimentos de soldagem de reparo para o aço 9Cr-1Mo Grau P9, que permitissem dispensar o tratamento térmico pós-soldagem (TTPS). Por meio de testes de simples deposição sobre chapa do metal de base previamente temperado (e não revenido) foram levantadas as condições ideais para a realização do reparo. O aço 9Cr-1Mo apresentou uma faixa de revenimento que representa cerca de 80% da extensão da ZAC endurecida. Em função disso, o calor gerado pela segunda camada não foi suficiente para tratar termicamente a ZAC endurecida da primeira, sendo necessário realizar um passe adicional de revenido com tocha TIG autógena. Nessas condições, conseguiu-se tratar totalmente a ZAC remanescente e se obter no estado como-soldado uma resistência ao impacto similar à do metal de base. Entretanto, os metais depositados com os consumíveis disponíveis comercialmente apresentaram no estado como-soldado uma tenacidade muito baixa, o que implica na necessidade de desenvolver eletrodos especiais que possam ser aplicados na soldagem de reparo sem TTPS.

Plasmid ColIb-P9 is a 93.2 kb self-transmissible plasmid, belonging to the I1 incompatibility group. Whilst much data had been gained concerning the molecular biology of conjugation mediated by this plasmid, a lack of information exsisted concerning the genetic organisation of the transfer genes. A physical map of the plasmid was constructed by detailed restriction analysis of DNA fragments sub-cloned from ColIb-P9. These fragments were also used to locate the positions of the transfer gene sog and the origin of transfer. Transposons Tn5 and Tnl723 were used to construct insertion mutants at defined points in ColIb-P9 and the effect of these on the expression of various transfer-related functions was studied. Using this technique, the probable location of the genes encoding the thick and thin sex pili were identified and also the site of the plasmid-encoded nuclease gene. The exact location of the entry exclusion gene was also determined. Complementation studies using the sub-cloned fragments of ColIb-P9 and a set of cosmid-clones generated from ColIbdrd-1 indicated that a positive regulator of the expression of the transfer genes exsisted and that this was composed of two genetically distinct elements. Studies involving wild type ColIb-P9 (drd+) indicated that this positive regulatory system is subject to negative control in cells containing the drd+ plasmid. The information gained from these studies was combined into a model of the organisation of the transfer genes of ColIb-P9. This defines at least three separate Tra regions, covering some 50 kb of the plasmid, with the origin of transfer located at one end of the transfer region.

L’objectif de cette thèse visait à améliorer la compréhension des mécanismes de contrôle des divisions méiotiques, un événement crucial en biologie de la reproduction et du développement. Il repose sur l’utilisation de l’ovocyte de Xénope, cellule bloquée en prophase de première division méiotique dans les ovaires. La reprise de la méiose a lieu lors de l’ovulation, en réponse à une hormone stéroïde, la progestérone. Elle se caractérise par la mise en place d'un premier fuseau de métaphase, l’expulsion du premier globule polaire et la formation du fuseau de métaphase de deuxième division méiotique, stade auquel l’ovocyte se bloque jusqu'à la fécondation. Le passage de la prophase I à la métaphase II est appelé maturation méiotique et est utilisé comme modèle d’étude de la transition G2-M du cycle cellulaire. La reprise de la méiose se caractérise par l’activation du MPF (M-phase Promoting Factor ou complexe Cdc2/Cycline B), facteur universel d’entrée en phase M chez les cellules eucaryotes. Nous nous sommes intéressés à l’étude des mécanismes régulant l’activation du MPF au cours de la reprise de la méiose. Cette activation repose sur la conversion du stock de pré-MPF inactif (stock de Cdc2/Cycline B maintenu inactif grâce à deux phosphorylations inhibitrices sur les résidus Thr14 et Tyr15 de Cdc2) en MPF actif, par un mécanisme d'auto-amplification. Pour que cet événement ait lieu un préalable est nécessaire : un changement d'équilibre des activités des enzymes régulant le niveau de phosphorylation des Thr14 et Tyr15 ; la phosphatase Cdc25 et la kinase Myt1. Dans un premier temps, nous avons montré que l’activité de Myt1 était indispensable dans le maintien des ovocytes en prophase I. Par la suite nous avons mis en évidence un mécanismes initiateur de l'entrée en méiose : des complexes de MPF actifs, nouvellement formés par les Cyclines synthétisées en réponse à la progestérone et du Cdc2 libre, prennent en charge l'inhibition initiale de Myt1, ce qui change l'équilibre Cdc25/Myt1 et lance la conversion du pré-MPF en MPF actif. Dans un deuxième temps, nous nous sommes intéressés à l’implication des protéines de la famille Cks, partenaires peu étudiés des Cdk/Cyclines, lors de la reprise de la méiose. Nous avons montré que la protéine Xe-p9, homologue de Cks chez le Xénope, forme un complexe avec un pool spécifique de la protéine Cdc2, non associée à une Cycline et phosphorylée sur le résidu Thr161. L'association de cette réserve spécifique de Cks/Cdc2 avec les Cyclines nouvellement synthétisées en réponse à la progestérone, aboutirait à la formation des néo-complexes de MPF actif, déjà phosphorylés sur la Thr161 et qui serviraient à lancer la boucle d'auto-amplification du MPF. Nos résultats suggèrent donc que la protéine Xe-p9 joue un rôle positif essentiel dans l'activation du MPF et l’initiation de la méiose dans l'ovocyte de Xénope
The main objective of this Thesis was to unravel the mechanisms allowing the activation of the molecular engine driving entry into M-phase in eukaryotic cells: MPF (M-Phase promoting Factor). For this purpose, meiotic divisions of the Xenopus oocytes were selected as a model system. Xenopus oocytes are naturally arrested in prophase of the first meiotic division. After progesterone stimulation, they complete the first meiotic division, form a metaphase I spindle and resume the first meiotic division with the extrusion of the first polar body. They immediately enter the second meiotic division by the formation of a metaphase II spindle and arrest at this stage until fertilization. This process depends the tight regulation of MPF activity (M-phase promoting factor), a complex between Cyclin B and the Cyclin-dependent kinase, Cdc2. Progesterone-triggered meiosis resumption ultimately leads to conversion of pre-MPF (a stockpile of inactive MPF due to two inhibitory phosphorylations, on Thr14 and Tyr15) into active MPF by an auto-amplification mechanism. MPF activation through removal of the inhibitory phosphorylations, is controlled by the activities of the Ccd25 phosphatase and the counteracting Myt1 kinase. The main results of this work are : 1) Myt1 function is required to maintain prophase I arrest in oocytes and Myt1 inhibition is an early event of meiosis resumption, controlled by neo-synthesized Cyclins, thus newly formed Cdc2/Cyclin B complexes. We propose a model in which the significant upregulation of Cyclin B synthesis following progesterone stimulation produces a small population of active Cdc2-Cyclin B, which is responsible for early Myt1 inhibition; this change in the balance between Cdc25 and Myt1 ensures rapid and complete conversion of pre-MPF into active MPF. 2) We then studied the implication of Cks proteins, Cdk-associated proteins, in the resumption of meiosis. We showed that the Xenopus Cks homolog Xe-p9 is present in oocytes and associated to a special fraction of free Cdc2, carrying the activating phosphorylation on Thr161. Furthermore, a functional approach allowed us to establish that Xe-p9 protein has an essential role in Xenopus meiotic M-phase entry. Overall our results led us to propose a model in which Cks-bound Cdc2, and already phosphorylated on Thr161, associates with newly synthesized Cyclins and the resulting active and ready-to-use MPF molecules act as the molecular trigger of meiosis re-entry

Le thème central de la thèse concerne l’utilisation des données de radio tracking pour le développement d’éphémérides planétaires, en particulier, dans deux cas : 1) analyse de données de navigation de la mission Cassini pour améliorer les éphémérides de Saturne et augmenter notre connaissance du système solaire externe ; 2) simulation des données radio de la mission ESA BepiColombo collectées durant la phase orbital à Mercure, pour évaluer leur contribution sur le développement des éphémérides planétaire de l’Intégrateur Numérique Planétaire de l’Observatoire de Paris (INPOP).Le premier sujet de recherche essaie de traiter les données de navigation de la sonde Cassini autour de Saturne en utilisant la connaissance mise à jour du système Saturnien : éphémérides précises pour les lunes du système et caractérisation de la gravité de Titan et des autres lunes principales.Ça permis la création des points normaux plus précis, capable de contraindre l’orbite de Saturne pour 13 ans (la moitié de sa révolution autour du Soleil) au niveau des mètres et de donner précieux informations sur le système solaire externe, en particulier sur la masse de la Kuiper belt et sur la possible position de P9. Les nouvelles données montrent une réduction de l’incertitude d’un facteur 5 en respect aux analyses précédentes.La deuxième partie de la thèse se concentre sur la production des simulations réalistes des données radio que le Mercury Orbiter Radio-science Experiment (MORE) de la sonde BepiColombo mesurera durant la phase scientifique de sa mission autour de Mercure.Des points normaux sont après produits avec une incertitude déduite de la matrice de covariance de l’état de la sonde estimé en utilisant ces données simulées.Ces points sont donc traités par le weighted-least square estimateur d’INPOP pour quantifier l’impact que les données de BepiColombo auront sur le développement des éphémérides planétaires, en particulier pour contraindre l’orbite de Mercure et des paramètres relativistes
The central theme of the thesis concerns the exploitation of radio tracking measurements for the development of planetary ephemerides, in particular, applied on two research topics: 1) the analysis of navigation data of Cassini mission to enhance the ephemeris of Saturn and increase our knowledge of the outer solar system; 2) the simulation of BepiColombo measurements collected during the orbital phase at Mercury, for assessing their contribution on the Intégrateur Numérique Planétaire de l’Observatoire de Paris (INPOP) planetary ephemerides.The first research aims at reprocessing Cassini radio tracking data by exploiting the current knowledge of the Saturnian system developed throughout the mission, i.e. the availability of accurate satellite ephemerides and precise gravity solutions for Saturn, Titan and the other major moons. This allows the production of more precise normal points, which are able to constrain the orbit of the planet at meters-level for 13 years (almost half of its revolution) and to provide invaluable insights on the mass of the Kuiper belt. The results show a reduction of a factor 5 on normal points uncertainties with respect to previous analyses, providing tighter constraints on the acceptance regions of planet 9.The second research topic focuses on the production of realistic normal points derived from the end-to-end simulation of BepiColombo Mercury Orbiter Radio-science Experiment (MORE). The uncertainties of the normal points are deduced from the mapped covariance of the spacecraft state. The derived measurements are then processed with the INPOP weighted-least squares filter to quantify the achievable constraints on ephemerides and relativistic parameters

Le cycle cellulaire est constitue de deux phases majeures, la phase s (replication de l'adn) et la phase m (division cellulaire). Celles-ci sont separees par deux periodes gap(g1 and g2). Le cycle cellulaire est hautement regule par les kinases cycline-dependantes (les cdk). La transition g2/m est declenchee par un facteur universel, le mpf m-phase promoting factor, identifie comme un complexe constitue d'au moins deux sous-unites, la p34#c#d#c#2 et la cycline b#c#d#c#1#3. L'entree de la cellule en phase m est caracterisee par une activation de la kinase cdc2 suite a une dephosphorylation sur les residus thr14 et tyr15. Cette dephosphorylation est catalysee par la phosphatase cdc25. Parmi les proteines regulant la formation et l'activation du complexe p34#c#d#c#2/cycline b, la p13#s#u#c#1/p9#c#k#s#h#s semble jouer un role fondamental. La p9#c#k#s#h#s interagit avec la p34#c#d#c#2 a travers deux sites cooperatifs conduisants a la formation d'un complexe p9#c#k#s#h#s/p34#c#d#c#2 tres stable. In vitro, la p9#c#k#s#h#s peut s'assembler en une structure hexamerique impliquant une possible oligomerisation de la p34#c#d#c#2 in vivo. Nous avons purifie une proteine de 15 kda, la p15#c#d#k#-#b#p, qui interagit fortement avec les kinases cdk4/cycline d (impliquee en g1) et cdk5/p25 (preferentiellement exprimee dans les tissus nerveux). La p15cdk-bp retient une kinase active envers les proteines chromosomales hmg i/y et p1 et la mbp myelin basic protein. Immobilisee sur des billes de sepharose, la p15#c#d#k#-#b#p peut constituer un outil important pour etudier la regulation du cycle cellulaire ainsi que la fonction et la pathologie du cerveau

碩士
明志科技大學
機械工程系機械與機電工程碩士班
107
This work explores mechanical properties, structural evolution, and mechanism of creep-life enhancement for widely used P9 heat-resistant steel.The 17-year-on-site used P9 alloy exhibit a higher tensile strength and a smaller elongation than the new P9 alloy from room temperature to 700oC.The P9 alloy also displays a typical ductile feature with a significantly necking profile.The P9 alloy shows phase transition sequences of α-Fe(bcc)→(Ac1~858℃)→α+γ-Fe(bcc+fcc)→(Ac3~894℃)→γ-Fe(fcc) upon heating and γ-Fe(fcc) →(Ms~352℃)→martensite(bct)→(Mf~300 ℃)→martensite(bct) upon cooling.The new P9-alloy tube mainly contains ~73.5% ferrite phase (α-Fe) and ~26.5% carbide M3C.However,the used P9-alloy tube shows four crystalline phases including ~45.9% ferrite, ~14.5% martensite, ~37.5% cementite (M3C) and ~2.7% carbide M23C6.The creep test indicates that the used P9-alloy tube has a longer creep-life (or better anti-creep ability) than the new tube.Activation energies of atomic diffusion for the new and used tubes are respectively 252.45 and 345.87 kJ/mol, indicating a decreased diffusion capability in the used tube. This work suggests that martensite laths, lath boundaries,and precipitates (such as carbides) play important roles to inhibit creep-deformation in the P9-alloy steel.