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Search Results: 1 - 10 of 2346 matches for " Guillaume Bossis "
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SUMO: regulating the regulator
Guillaume Bossis, Frauke Melchior
Cell Division , 2006, DOI: 10.1186/1747-1028-1-13
Abstract: Sumoylation, which consists in the covalent and reversible conjugation of Small Ubiquitin-related Modifiers (SUMO-1, 2 and 3 in mammals) to target proteins, is an essential cellular process from yeasts to mammals. In S. cerevisiae, disruption of the SUMO pathway leads to a G2/M cell cycle arrest [1]; In mouse, it leads to embryonic death at early stages [2].The number of known SUMO targets is growing exponentially, and it seems likely that this modification is as common as phosphorylation to regulate biological processes [3]. Most SUMO targets were initially found in the nucleus, but it is now clear that sumoylation also regulates cytoplasmic-, and even plasma membrane associated proteins. Modification has been linked to pathways as diverse as intracellular trafficking, cell cycle, DNA repair and replication, RNA metabolism and cell signalling (for detailed description of sumoylation functions see [4]). At a molecular level, sumoylation alters protein functions by masking and/or adding interaction surfaces, or by inducing conformational changes that result in altered interactions (for detailed examples see [5]). As a consequence, a wide variety of downstream consequences have been observed, including changes in localisation, enzymatic activity, or stability.Among the many known targets of sumoylation, a large number are regulators of gene expression, in particular transcription factors, co-activators or repressors. Here, the emerging picture is that sumoylation essentially results in down-regulation of gene expression. Albeit the molecular mechanisms underlying this repression by SUMO are still ill defined, they seem to involve SUMO-dependent recruitment of transcriptional repressors such as HDACs directly to promoters [6].All SUMO isoforms are conjugated via a conserved enzymatic cascade that resembles that of ubiquitin conjugation (Figure 1). SUMO is first activated by formation of a thioester bond between its C-terminal glycine and the catalytic cysteine of the h
Transcriptional Activation of the Adenoviral Genome Is Mediated by Capsid Protein VI
Sabrina Schreiner,Ruben Martinez,Peter Groitl,Fabienne Rayne,Remi Vaillant,Peter Wimmer,Guillaume Bossis,Thomas Sternsdorf,Lisa Marcinowski,Zsolt Ruzsics,Thomas Dobner,Harald Wodrich
PLOS Pathogens , 2012, DOI: 10.1371/journal.ppat.1002549
Abstract: Gene expression of DNA viruses requires nuclear import of the viral genome. Human Adenoviruses (Ads), like most DNA viruses, encode factors within early transcription units promoting their own gene expression and counteracting cellular antiviral defense mechanisms. The cellular transcriptional repressor Daxx prevents viral gene expression through the assembly of repressive chromatin remodeling complexes targeting incoming viral genomes. However, it has remained unclear how initial transcriptional activation of the adenoviral genome is achieved. Here we show that Daxx mediated repression of the immediate early Ad E1A promoter is efficiently counteracted by the capsid protein VI. This requires a conserved PPxY motif in protein VI. Capsid proteins from other DNA viruses were also shown to activate the Ad E1A promoter independent of Ad gene expression and support virus replication. Our results show how Ad entry is connected to transcriptional activation of their genome in the nucleus. Our data further suggest a common principle for genome activation of DNA viruses by counteracting Daxx related repressive mechanisms through virion proteins.
Synthesis and Surface Modification of Spindle-Type Magnetic Nanoparticles: Gold Coating and PEG Functionalization  [PDF]
Juan Mendez-Garza, Biran Wang, Alexandra Madeira, Christophe Di Giorgio, Georges Bossis
Journal of Biomaterials and Nanobiotechnology (JBNB) , 2013, DOI: 10.4236/jbnb.2013.43027
Abstract:

In this paper, we describe the synthesis of gold coated spindle-type iron nanoparticles and its surface modification by a thiolated fluorescently-labelled polyethylene glycol (PEG) polymer. A forced hydrolysis of ferric salts in the presence of phosphate ions was used to produce α-Fe2O3 spindle-type particles. The oxide powders were first reduced to α-iron under high temperature and controlled dihydrogen atmosphere. Then, the resulting magnetic spindle-type particles were covered by a shell of gold. The formation of the core@shell structure was driven by a redox-transmetalation reaction between iron(0) at the surface of particles and a gold(III) salt. Protected against oxidation, the Fe@Au core@shell nanoparticles were then grafted with a water soluble fluorescent-PEG-thiol. TEM, XRD, EDX and measurements of magnetic properties of particles confirm 1) the conversion of hematite into iron and 2) their subsequent surface protection with a gold shell. Furthermore, the functionalization of the gold nanoparticle surface with a PEG carrying a fluorescent dye was unambiguously attested by confocal laser scanning microscopy.

Granular Rheology in Zero Gravity
G. Bossis,Y. Grasselli,O. Volkova
Physics , 2003, DOI: 10.1088/0953-8984/16/18/027
Abstract: We present an experimental investigation on the rheological behavior of model granular media made of nearly elastic spherical particles. The experiments are performed in a cylindrical Couette geometry and the experimental device is placed inside an airplane undergoing parabolic flights to cancel the effect of gravity. The corresponding curves, shear stress versus shear rate, are presented and a comparison with existing theories is proposed. The quadratic dependence on the shear rate is clearly shown and the behavior as a function of the solid volume fraction of particles exhibits a power law function. It is shown that theoretical predictions overestimate the experiments. We observe, at intermediate volume fractions, the formation of rings of particles regularly spaced along the height of the cell. The differences observed between experimental results and theoretical predictions are discussed and related to the structures formed in the granular medium submitted to the external shear.
Translational and rotational temperatures of a 2D vibrated granular gas in microgravity
Yan Grasselli,Georges Bossis,Romain Morini
Physics , 2014,
Abstract: We present an experimental study performed on a vibrated granular gas enclosed into a 2D rectangular cell. Experiments are realized in microgravity. High speed video recording and optical tracking allow to obtain the full kinematics (translation and rotation) of the particles. The inelastic parameters are retrieved from the experimental trajectories as well as the translational and rotational velocity distributions. We report that the experimental ratio of translational versus rotational temperature decreases to the density of the medium but increases with the driving velocity of the cell. These experimental results are compared with existing theories and we point out the differences observed. We also present a model which fairly predicts the equilibrium experimental temperatures along the direction of vibration.
Theoretical and Numerical Comparison of Limit Point Bifurcation and Maximum Force Criteria. Application to the Prediction of Diffuse Necking  [PDF]
Guillaume Altmeyer
Modeling and Numerical Simulation of Material Science (MNSMS) , 2013, DOI: 10.4236/mnsms.2013.31006
Abstract: A large number of criteria has been developed to predict material instabilities, but their choice is limited by the lack of existing comparison of their theoretical basis and application domains. To overcome this limitation, a theoretical and numerical comparison of two major models used to predict diffuse necking is present in this paper. Limit Point Bifurcation criterion is first introduced. An original formulation of the Maximum Force Criterion (MFC), taking into account the effects of damage and isotropic and kinematic hardenings, is then proposed. Strong connections are shown between them by comparing their theoretical basis. Numerical Forming Limit Diagrams at diffuse necking obtained with these criteria for different metallic materials are given. They illustrate the theoretical link and similar predictions are shown for both models.
Viral FLICE Inhibitory Protein of Rhesus Monkey Rhadinovirus Inhibits Apoptosis by Enhancing Autophagosome Formation
Krit Ritthipichai, Yuchen Nan, Ioannis Bossis, Yanjin Zhang
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0039438
Abstract: Rhesus monkey rhadinovirus (RRV) is a gamma-2 herpesvirus closely related to human herpesvirus 8 (HHV8). RRV encodes viral FLICE inhibitory protein (vFLIP), which has death effector domains. Little is known about RRV vFLIP. This study intended to examine its function in apoptosis. Here we found that RRV vFLIP inhibits apoptosis induced by tumor necrosis factor-α (TNF-α) and cycloheximide. In HeLa cells with vFLIP expression, the cleavage of poly [ADP-ribose] polymerase 1 (PARP-1) and activities of caspase 3, 7, and 9 were much lower than those in controls. Cell viability of HeLa cells with vFLIP expression was significantly higher than control cells after apoptosis induction. However, RRV vFLIP appears unable to induce NF-κB signaling when tested in NF-κB reporter assay. RRV vFLIP was able to enhance cell survival under starved conditions or apoptosis induction. At early time points after apoptosis induction, autophagosome formation was enhanced and LC3-II level was elevated in cells with vFLIP and, when autophagy was blocked with chemical inhibitors, these cells underwent apoptosis. Moreover, RRV latent infection of BJAB B-lymphoblastoid cells protects the cells against apoptosis by enhancing autophagy to maintain cell survival. Knockdown of vFLIP expression in the RRV-infected BJAB cells with siRNA abolished the protection against apoptosis. These results indicate that vFLIP protects cells against apoptosis by enhancing autophagosome formation to extend cell survival. The finding of vFLIP’s inhibition of apoptosis via the autophagy pathway provides insights of vFLIP in RRV pathogenesis.
Non-simplifying Graph Rewriting Termination
Guillaume Bonfante,Bruno Guillaume
Electronic Proceedings in Theoretical Computer Science , 2013, DOI: 10.4204/eptcs.110.3
Abstract: So far, a very large amount of work in Natural Language Processing (NLP) rely on trees as the core mathematical structure to represent linguistic informations (e.g. in Chomsky's work). However, some linguistic phenomena do not cope properly with trees. In a former paper, we showed the benefit of encoding linguistic structures by graphs and of using graph rewriting rules to compute on those structures. Justified by some linguistic considerations, graph rewriting is characterized by two features: first, there is no node creation along computations and second, there are non-local edge modifications. Under these hypotheses, we show that uniform termination is undecidable and that non-uniform termination is decidable. We describe two termination techniques based on weights and we give complexity bound on the derivation length for these rewriting system.
Chaining in Magnetic Colloids in the Presence of Flow
I. Perez-Castillo,A. Perez-Madrid,J. M. Rubi,G. Bossis
Physics , 2000, DOI: 10.1063/1.1308541
Abstract: We discuss the effect of an homogeneous flow in the aggregation process of colloidal magnetic particles at moderate concentration. Situations in which the presence of flow acts in favor of the chaining process: particles assemble into chains larger than the ones emerging in the absence of flow, under the only influence of an externnaly imposed field, have been analyzed. The results we obtain follow from the analysis of the pair correlation function which, owing to the potencial character of the flow we consider, can be interpreted in terms of a Boltzmann-like stationary distribution function. To render the influence of the flow on the resulting structures explicit, we study the particular cases of axisymmetric and planar elongational flows.
Données complémentaires sur les besoins nutritionnels de la reproductrice naine ? Vedette I.N.R.A. JV 15 ?
J Guillaume
Genetics Selection Evolution , 1971, DOI: 10.1186/1297-9686-3-3-390
Abstract:
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