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Search Results: 1 - 10 of 462704 matches for " Martine A. Collart "
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The Not4 RING E3 Ligase: A Relevant Player in Cotranslational Quality Control
Martine A. Collart
ISRN Molecular Biology , 2013, DOI: 10.1155/2013/548359
The Not4 RING E3 Ligase: A Relevant Player in Cotranslational Quality Control
Martine A. Collart
ISRN Molecular Biology , 2013, DOI: 10.1155/2013/548359
Abstract: The Not4 RING E3 ligase is a subunit of the evolutionarily conserved Ccr4-Not complex. Originally identified in yeast by mutations that increase transcription, it was subsequently defined as an ubiquitin ligase. Substrates for this ligase were characterized in yeast and in metazoans. Interestingly, some substrates for this ligase are targeted for polyubiquitination and degradation, while others instead are stable monoubiquitinated proteins. The former are mostly involved in transcription, while the latter are a ribosomal protein and a ribosome-associated chaperone. Consistently, Not4 and all other subunits of the Ccr4-Not complex are present in translating ribosomes. An important function for Not4 in cotranslational quality control has emerged. In the absence of Not4, the total level of polysomes is reduced. In addition, translationally arrested polypeptides, aggregated proteins, and polyubiquitinated proteins accumulate. Its role in quality control is likely to be related on one hand to its importance for the functional assembly of the proteasome and on the other hand to its association with the RNA degradation machines. Not4 is in an ideal position to signal to degradation mRNAs whose translation has been aborted, and this defines Not4 as a key player in the quality control of newly synthesized proteins. 1. Introduction The appropriate control of gene expression is essential to the development and growth of all organisms. Ultimately, gene expression is the production of functional proteins at the appropriate time and level, in their appropriate cellular localization and state for interaction with their correct physiological partners. Many things can go wrong between transcription of a gene and this ultimate goal. Sophisticated surveillance mechanisms have therefore evolved to follow gene expression at every step and destroy aberrant products whose accumulation can be toxic, leading ultimately to cell death. Proteins mediate almost all cellular functions. Hence one crucial step in the expression of a gene is the synthesis of its encoded polypeptide at the ribosome. This process involves many interactions, constraints, modifications, and precisely defined kinetics of synthesis. Multiple quality control systems ensure that the newly synthesized proteins ultimately achieve their native functional form, or if they do not, they get removed and destroyed. This paper will summarize the different components that contribute to this quality control system and present a new and relevant player, the Not4 RING E3 ligase. 2. Folding of Newly Synthesized Polypeptides
The CCR4-NOT Complex Physically and Functionally Interacts with TRAMP and the Nuclear Exosome
Nowel Azzouz, Olesya O. Panasenko, Geoffroy Colau, Martine A. Collart
PLOS ONE , 2009, DOI: 10.1371/journal.pone.0006760
Abstract: Background Ccr4-Not is a highly conserved multi-protein complex consisting in yeast of 9 subunits, including Not5 and the major yeast deadenylase Ccr4. It has been connected functionally in the nucleus to transcription by RNA polymerase II and in the cytoplasm to mRNA degradation. However, there has been no evidence so far that this complex is important for RNA degradation in the nucleus. Methodology/Principal Findings In this work we point to a new role for the Ccr4-Not complex in nuclear RNA metabolism. We determine the importance of the Ccr4-Not complex for the levels of non-coding nuclear RNAs, such as mis-processed and polyadenylated snoRNAs, whose turnover depends upon the nuclear exosome and TRAMP. Consistently, mutation of both the Ccr4-Not complex and the nuclear exosome results in synthetic slow growth phenotypes. We demonstrate physical interactions between the Ccr4-Not complex and the exosome. First, Not5 co-purifies with the exosome. Second, several exosome subunits co-purify with the Ccr4-Not complex. Third, the Ccr4-Not complex is important for the integrity of large exosome-containing complexes. Finally, we reveal a connection between the Ccr4-Not complex and TRAMP through the association of the Mtr4 helicase with the Ccr4-Not complex and the importance of specific subunits of Ccr4-Not for the association of Mtr4 with the nuclear exosome subunit Rrp6. Conclusions/Significance We propose a model in which the Ccr4-Not complex may provide a platform contributing to dynamic interactions between the nuclear exosome and its co-factor TRAMP. Our findings connect for the first time the different players involved in nuclear and cytoplasmic RNA degradation.
The Not4 E3 Ligase and CCR4 Deadenylase Play Distinct Roles in Protein Quality Control
David Halter, Martine A. Collart, Olesya O. Panasenko
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0086218
Abstract: Eukaryotic cells control their proteome by regulating protein production and protein clearance. Protein production is determined to a large extent by mRNA levels, whereas protein degradation depends mostly upon the proteasome. Dysfunction of the proteasome leads to the accumulation of non-functional proteins that can aggregate, be toxic for the cell, and, in extreme cases, lead to cell death. mRNA levels are controlled by their rates of synthesis and degradation. Recent evidence indicates that these rates have oppositely co-evolved to ensure appropriate mRNA levels. This opposite co-evolution has been correlated with the mutations in the Ccr4-Not complex. Consistently, the deadenylation enzymes responsible for the rate-limiting step in eukaryotic mRNA degradation, Caf1 and Ccr4, are subunits of the Ccr4-Not complex. Another subunit of this complex is a RING E3 ligase, Not4. It is essential for cellular protein solubility and has been proposed to be involved in co-translational quality control. An open question has been whether this role of Not4 resides strictly in the regulation of the deadenylation module of the Ccr4-Not complex. However, Not4 is important for proper assembly of the proteasome, and the Ccr4-Not complex may have multiple functional modules that participate in protein quality control in different ways. In this work we studied how the functions of the Caf1/Ccr4 and Not4 modules are connected. We concluded that Not4 plays a role in protein quality control independently of the Ccr4 deadenylase, and that it is involved in clearance of aberrant proteins at least in part via the proteasome.
The Ccr4-Not Complex Interacts with the mRNA Export Machinery
Shana C. Kerr,Nowel Azzouz,Stephen M. Fuchs,Martine A. Collart,Brian D. Strahl,Anita H. Corbett,R. Nicholas Laribee
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0018302
Abstract: The Ccr4-Not complex is a key eukaryotic regulator of gene transcription and cytoplasmic mRNA degradation. Whether this complex also affects aspects of post-transcriptional gene regulation, such as mRNA export, remains largely unexplored. Human Caf1 (hCaf1), a Ccr4-Not complex member, interacts with and regulates the arginine methyltransferase PRMT1, whose targets include RNA binding proteins involved in mRNA export. However, the functional significance of this regulation is poorly understood.
The Not5 Subunit of the Ccr4-Not Complex Connects Transcription and Translation
Zoltan Villanyi,Virginie Ribaud,Sari Kassem,Olesya O. Panasenko,Zoltan Pahi,Ishaan Gupta,Lars Steinmetz,Imre Boros,Martine A. Collart
PLOS Genetics , 2014, DOI: doi/10.1371/journal.pgen.1004569
Abstract: Recent studies have suggested that a sub-complex of RNA polymerase II composed of Rpb4 and Rpb7 couples the nuclear and cytoplasmic stages of gene expression by associating with newly made mRNAs in the nucleus, and contributing to their translation and degradation in the cytoplasm. Here we show by yeast two hybrid and co-immunoprecipitation experiments, followed by ribosome fractionation and fluorescent microscopy, that a subunit of the Ccr4-Not complex, Not5, is essential in the nucleus for the cytoplasmic functions of Rpb4. Not5 interacts with Rpb4; it is required for the presence of Rpb4 in polysomes, for interaction of Rpb4 with the translation initiation factor eIF3 and for association of Rpb4 with mRNAs. We find that Rpb7 presence in the cytoplasm and polysomes is much less significant than that of Rpb4, and that it does not depend upon Not5. Hence Not5-dependence unlinks the cytoplasmic functions of Rpb4 and Rpb7. We additionally determine with RNA immunoprecipitation and native gel analysis that Not5 is needed in the cytoplasm for the co-translational assembly of RNA polymerase II. This stems from the importance of Not5 for the association of the R2TP Hsp90 co-chaperone with polysomes translating RPB1 mRNA to protect newly synthesized Rpb1 from aggregation. Hence taken together our results show that Not5 interconnects translation and transcription.
Bleustein-Gulyaev SAWS with Low Losses: Approximate Direct Solution  [PDF]
Martine Rousseau, Gérard A. Maugin
Journal of Electromagnetic Analysis and Applications (JEMAA) , 2011, DOI: 10.4236/jemaa.2011.34020
Abstract: The main properties (attenuation along the surface, attenuation in depth, additional radiation in depth, dispersion in propagation space) of Bleustein-Gulyaev surface acoustic waves (SAWs) in electroelasticity are determined in terms of a perturbation due to viscosity. This paves the way for a study of the perturbed motion of associated quasi-particles in the presence of low losses.
La pedagogie interculturelle: entre multiculturalisme et universalisme
Martine A. Pretceille
Linguarum Arena : Revista do Programa Doutoral em Didáctica de Línguas da Universidade do Porto , 2011,
Abstract: The author intends to show that intercultural education is characterized by two conflicting approaches - an exacerbation of differences, and a universalism that, unfortunately, tends to be confused with the ethical principle of universality. Indeed, the treatment of cultural heterogeneity implies lean analysis and action from a moral and pragmatic philosophical viewpoint, that understands the practices, discourses and behaviours as rooted not in culturally distinct, homogeneous and hermetic categories, but rather as part of a process of miscegenation and “creolization”. Learning to observe, listen, and be attentive to others is the way in which we experience otherness, while avoiding what one may call the “learning of a culture”. This experience has to be acquired and developed. Thus, taking into account culture does not mean the mere introduction of an additional variable, but mainly aims to build up a humanism of the otherness.
The law pertaining to food issues and natural resources exploitation and trade
Francois Collart Dutilleul
Agriculture & Food Security , 2012, DOI: 10.1186/2048-7010-1-6
Abstract: We wish to determine the appropriate way to determine a law on natural resources that preserves on every continent the food safety. This safety supposes that the agricultural and feeding purposes of the land be maintained, that farmers and their families can access the land and live decently from it and that access to healthy food in sufficient supplying be guaranteed to everyone.None of the objectives will be achieved without the law conveying the values that society will choose for itself. Between the law and the contract, collective security and individual freedom or between State sovereignty and globalization of trade, one must think of a humanist law to help the Earth to feed Humanity.
GIS and Multi-Criteria Decision Analysis for Land Use Resource Planning  [PDF]
Martine Nyeko
Journal of Geographic Information System (JGIS) , 2012, DOI: 10.4236/jgis.2012.44039
Abstract: Natural resources management is indispensable in ensuring environmental sustainability and reducing the risk associated with climate change and increasing demand for ecological goods and services. Natural resources planners need to have at their disposal tools that can objectively help in prioritizing land use allocation. Traditional application of land use change model based on economic model, trend analysis, and or scenario analysis present some challenges of data availability and reliability necessary for implementation of the models. However, with the advent of information technology, GIS and remote sensing, biophysical data known for having influence on land use allocation can easily be accessed. The current study explores the application of GIS-Multi-criteria analysis in modeling future land use scenarios for resources planning and management using easy to construct biophysical parameters known for influencing future land use allocation. The decision problems in this study are to find the best spatial allocation of land to future agriculture and forest development, which are considered to present critical land use change in the study area. The afforestation scenarios are meant to offset the pressure on the native forest resources due to the increased demand for fuel and timber and also to contribute to the environmental protection and the agricultural land use scenarios are meant to increase productivity and ensure environmental protection. The land use scenarios did not consider “when” in the future the land use pattern may develop. The analyses of scenarios indicate that afforestation extent in the basin can be increased from 4.6% to 42.9% of the total basin area. However, the afforestation extent of 42.9% may be considered unrealistic, since in practice, it may not be possible to realize up to 42.9% afforestation, nevertheless, the spatial pattern of the afforestation may provide crucial insight into spatial afforestation policies and it future consequences. The agricultural land use can increase from 6.2% to 53.7% of the basin area. The agricultural land use expansion can be realised since the expansion of farm land is primarily the main option to achieve food production increase in the near future. The findings indicate potential use of the methodology in land use planning.
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