Sticking temperature investigations of glass/metal contacts Determination of influencing parameters

Sticking experiments between hot viscous glass and metallic Substrates have been performed with a glass press apparatus on a laboratory scale, allowing a precise determination of the sticking temperatures, Ts, versus selected experimental parameters (nature of the Substrate, composition of the glass). Complementary surface analyses have also been carried out to identify the surface and interface reaction products following the glass/metal contact. Experimental results have been compared to ternary phase diagrams, in order to test the reliability of thermodynamic calculations to predict the nature of the phases produced by the contact at high temperature. The sticking phenomenon is governed by a coupling between the rheological behaviour of the glass melt and the physicochemical reactivity of the contacting surfaces. Sticking occurs when the temperature at the interface remains sufficiently high, so that the glass viscosity remains low enough to enhance the real contact area and thus, to induce physicochemical interactions between Substrate and glass. Sticking is attributed to the presence of an interfacial oxide layer which strongly adheres onto the glass. Chemical analysis of the sticking surfaces identifies a physicochemical driving force contributing to the sticking phenomenon. The predominant reaction consists in the reduction of the sodium oxide of the glass at the expense of the oxidation of the metallic elements of the Substrate during pressing, in agreement with thermochemical calculations presented by the ternary phase diagrams. The strong chemical reactivity of the soda-lime-silica glass is thus attributed in particular to the highly reactive sodium oxide constituent

Structure and function of the yeast listerin (ltn1) conserved N-terminal domain In binding to stalled 60s ribosomal subunits

The Ltn1 E3 ligase (listerin in mammals) has emerged as a paradigm for understanding ribosome-associated ubiquitylation. Ltn1 binds to 60S ribosomal subunits to ubiquitylate nascent polypeptides that become stalled during synthesis; among Ltn1's substrates are aberrant products of mRNA lacking stop codons [nonstop translation products (NSPs)]. Here, we report the reconstitution of NSP ubiquitylation in Neurospora crassa cell extracts. Upon translation in vitro, ribosome-stalled NSPs were ubiquitylated in an Ltn1-dependent manner, while still ribosome-associated. Furthermore, we provide biochemical evidence that the conserved N-terminal domain (NTD) plays a significant role in the binding of Ltn1 to 60S ribosomal subunits and that NTD mutations causing defective 60S binding also lead to defective NSP ubiquitylation, without affecting Ltn1's intrinsic E3 ligase activity. Finally, we report the crystal structure of the Ltn1 NTD at 2.4-angstrom resolution. The structure, combined with additional mutational studies, provides insight to NTD's role in binding stalled 60S subunits. Our findings show that Neurospora extracts can be used as a tool to dissect mechanisms underlying ribosome-associated protein quality control and are consistent with a model in which Ltn1 uses 60S subunits as adapters, at least in part via its NTD, to target stalled NSPs for ubiquitylation.The Ltn1 E3 ligase (listerin in mammals) has emerged as a paradigm for understanding ribosome-associated ubiquitylation. Ltn1 binds to 60S ribosomal subunits to ubiquitylate nascent polypeptides that become stalled during synthesisamong Ltn1's substra11329E4151E4160sem informaçãosem informaçãoWe thank G. Dieci and J. Warner for reagents and the Fungal Genetics Stock Center for providing Neurospora strains. Work in the C.A.P.J. laboratory is supported by R01 Grant NS075719 from the National Institute of Neurological Disorders and Stroke (NIND

The C-terminal domain from S. cerevisiae Pat1 displays two conserved regions involved in decapping factor recruitment

Eukaryotic mRNA decay is a highly regulated process allowing cells to rapidly modulate protein production in response to internal and environmental cues. Mature translatable eukaryotic mRNAs are protected from fast and uncontrolled degradation in the cytoplasm by two cis-acting stability determinants: a methylguanosine (m(7)G) cap and a poly(A) tail at their 5' and 3' extremities, respectively. The hydrolysis of the m(7)G cap structure, known as decapping, is performed by the complex composed of the Dcp2 catalytic subunit and its partner Dcp1. The Dcp1-Dcp2 decapping complex has a low intrinsic activity and requires accessory factors to be fully active. Among these factors, Pat1 is considered to be a central scaffolding protein involved in Dcp2 activation but also in inhibition of translation initiation. Here, we present the structural and functional study of the C-terminal domain from S. cerevisiae Pat1 protein. We have identified two conserved and functionally important regions located at both extremities of the domain. The first region is involved in binding to Lsm1-7 complex. The second patch is specific for fungal proteins and is responsible for Pat1 interaction with Edc3. These observations support the plasticity of the protein interaction network involved in mRNA decay and show that evolution has extended the C-terminal alpha-helical domain from fungal Pat1 proteins to generate a new binding platform for protein partners

Specific Evolution of F1-Like ATPases in Mycoplasmas

F1F0 ATPases have been identified in most bacteria, including mycoplasmas which have very small genomes associated with a host-dependent lifestyle. In addition to the typical operon of eight genes encoding genuine F1F0 ATPase (Type 1), we identified related clusters of seven genes in many mycoplasma species. Four of the encoded proteins have predicted structures similar to the α, β, γ and ε subunits of F1 ATPases and could form an F1-like ATPase. The other three proteins display no similarity to any other known proteins. Two of these proteins are probably located in the membrane, as they have three and twelve predicted transmembrane helices. Phylogenomic studies identified two types of F1-like ATPase clusters, Type 2 and Type 3, characterized by a rapid evolution of sequences with the conservation of structural features. Clusters encoding Type 2 and Type 3 ATPases were assumed to originate from the Hominis group of mycoplasmas. We suggest that Type 3 ATPase clusters may spread to other phylogenetic groups by horizontal gene transfer between mycoplasmas in the same host, based on phylogeny and genomic context. Functional analyses in the ruminant pathogen Mycoplasma mycoides subsp. mycoides showed that the Type 3 cluster genes were organized into an operon. Proteomic analyses demonstrated that the seven encoded proteins were produced during growth in axenic media. Mutagenesis and complementation studies demonstrated an association of the Type 3 cluster with a major ATPase activity of membrane fractions. Thus, despite their tendency toward genome reduction, mycoplasmas have evolved and exchanged specific F1-like ATPases with no known equivalent in other bacteria. We propose a model, in which the F1-like structure is associated with a hypothetical X0 sector located in the membrane of mycoplasma cells

Eric Wauters. Noël de La Marinière (1765-1822): culture, sensibilité et sociabilité entre l'Ancien Régime et la Restauration

Charenton Benoît. Eric Wauters. Noël de La Marinière (1765-1822): culture, sensibilité et sociabilité entre l'Ancien Régime et la Restauration . In: Bibliothèque de l'école des chartes. 2002, tome 160, livraison 1. pp. 333-334

Evolution and functional characterization of a F1-likeX0 ATPase specific of mycoplasmas

Les ATPases F1F0 sont présentes chez la majorité des bactéries, notamment les mycoplasmes qui sont caractérisés par un génome réduit et un mode de vie parasitaire. En plus de l’opéron codant l’ATPase F1F0, des clusters apparentés de sept gènes ont été identifiés dans le génome de nombreux mycoplasmes. Au cours de cette thèse, nous avons cherché à caractériser l’évolution et la fonction de ces clusters supplémentaires. Quatre des protéines codées par ces clusters présentent des similarités structurales avec les sous-unités α, β, et ε de l’ATPase F1F0, résultant en une potentielle structure F1-like. Les trois autres protéines ne présentent aucune similarité avec des protéines connues. Une localisation transmembranaire est prédite pour deux d’entre elles. Deux types d’ATPase F1-like, Type 2 et Type 3, ont été identifiés. Les clusters de Type 2 et de Type 3 pourraient être originaires du groupe phylogénétique Hominis, les clusters de Type 3 ayant vraisemblablement été disséminés par des transferts horizontaux de gènes entre mycoplasmes colonisant le même hôte. Les gènes du cluster de Type 3 de Mycoplasma mycoides subsp. mycoides sont organisés en opéron et exprimés en milieu axénique. Des études de mutagénèse et de complémentation démontrent que le cluster de Type 3 est associé à une activité ATPase majeure des fractions membranaires. Des analyses biochimiques suggèrent que l’activité ATPase du cluster est sensible au ∆pH mais pas au ∆Ψ. Ces analyses suggèrent que le sodium et le potassium ne sont pas impliqués dans le fonctionnement de l’ATPase F1-likeX0. Les sous-unités des ATPases F1-likeX0 et F1F0 présentent un comportement différent en présence de détergents. L’ensemble de ces expériences suggèrent que l’ATPase F1-likeX0 est un complexe plus fragile que l’ATPase F1F0. Nos résultats montrent qu’en dépit d’une tendance à la réduction de génome, les mycoplasmes ont développé et échangé des ATPases sans équivalent chez d’autres bactéries. Nous proposons un modèle dans lequel une structure F1-like est associée avec un domaine hypothétique X0, enchâssé dans la membrane des mycoplasmes.F1F0 ATPases have been found in most bacteria, including mycoplasmas that are characterized by drastically reduced genomes and a parasitic lifestyle. In addition to the typical operon of eight genes encoding genuine F1F0 ATPase, related clusters of seven genes were identified in many mycoplasmas. In this work, we investigated the evolution and the function of these supplementary clusters. Four proteins encoded by these clusters present structural similarities with subunits α, β, and ε of F1F0 ATPases, resulting in potential F1-like structures. The three other encoded proteins did not show any similarity to known proteins. Transmembrane helices were predicted for two of them, suggesting a membrane localisation. Two types of F1-like ATPases, Type 2 and Type 3, were identified. Clusters encoding Type 2 and Type 3 ATPases were assumed to originate from the Hominis group of mycoplasmas. Further spreading of Type 3 ATPases towards other phylogenetic groups by horizontal gene transfers in between mycoplasmas sharing a same host was proposed on the basis of phylogenetic trees and genomic context. Functional analyses indicated that genes of Type 3 cluster in the ruminant pathogen Mycoplasma mycoides subsp. mycoides were organized as an operon. Proteomic analyses indicated that the seven encoded proteins were produced during growth in axenic media. Mutagenesis and complementation assays demonstrated that Type 3 cluster was associated with a major ATPase activity of membrane fractions. Biochemical analyses indicated that this ATPase activity was sensitive to ΔpH but not to ΔΨ. These analyses suggested that Na+ and K+ were not involved in the F1-likeX0 functioning. Our results indicated a behaviour of F1-likeX0 ATPase subunits that is different to that of F1F0 ATPase subunits in presence of detergents. Altogether, these analyses suggest that the F1-likeX0 complex could be more fragile than the F1F0 complex. Our results showed that despite their tendency to genome reduction, mycoplasmas have evolved and exchanged specific F1-like ATPases with no known equivalent in other bacteria. We propose a model in which the F1-like structure is associated with a hypothetical X0 sector embedded in the membrane of mycoplasmal cells

Pédagogie pratique

Charenton L. Pédagogie pratique. In: Manuel général de l'instruction primaire : journal hebdomadaire des instituteurs. 77e année, tome 46, 1909. p. 423

En Classe

Charenton L. En Classe. In: Manuel général de l'instruction primaire : journal hebdomadaire des instituteurs. 76e année, tome 45, 1908. p. 100

Bassins d'orage et noues : connaître le patrimoine de Nantes Métropole pour favoriser la biodiversité dans la gestion et la conception des ouvrages

Urbanized areas have to deal with stormwater management. In the last few years, alternative techniques have been set up, aiming at a change in management habits. Stormwater ponds and swales are two of them, and they seem to be suited for an integrated management, including biodiversity. An approach of these two techniques has been introduced in Nantes Métropole, for a better knowing of these devices in order to apply a suited management. Different objectives have been led for this work. First of all, an inventory of the devices on Nantes Métropole's territory and a management survey has been undertaken. After the study of the informations, principles for organisation, management and conception have been suggested. At the same time, the theme of the biodiversity has been included in every part of the work. In order to guarantee efficiency to the whole approach, the work will be continued in Nantes Métropole for the years to come.La gestion des eaux pluviales en ville fait partie des grands enjeux de l'urbanisation. Dans ce cadre, des techniques de gestion dites alternatives, proposant de nouvelles perspectives ont été mises en place. Parmi elles, les bassins d'orage et les noues semblent bien adaptés à une gestion intégrée au contexte, et permettant notamment de favoriser la biodiversité. À l'initiative de la communauté urbaine de Nantes Métropole, un travail sur ce sujet a été lancé, pour aboutir à une meilleure connaissance de ces ouvrages et y appliquer une gestion appropriée. La démarche, articulée autour de plusieurs objectifs, se compose de différentes étapes. En premier lieu, un recensement des ouvrages sur le territoire métropolitain ainsi qu'une enquête sur les pratiques de gestion ont été effectués. Une fois ces informations analysées, des principes portant sur l'organisation de la prise en charge de ces ouvrages, ainsi qui des préconisations de gestion différenciée et de conception ont pu être élaborés. En parallèle, une réflexion sur l'intégration de la biodiversité à la démarche a été conduite, permettant d'intégrer cette thématique à l'ensemble du travail. Pour garantir le suivi et la bonne prise en compte des bassins d'orage et des noues, cette action sera poursuivie au sein de Nantes Métropole dans les années à venir