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Genome-scale engineering enables rational removal of dispensable genes in chassis genomes. Deviating from this approach, we applied greedy accumulation of deletions of large dispensable regions in the Bacillus subtilis genome, yielding a library of 298 strains with genomes reduced up to 1.48 Mb in size. High-throughput physiological phenotyping of these strains confirmed that genome reduction is associated with substantial loss of cell fitness and accumulation of synthetic-sick interactions. Transcriptome analysis indicated that 300-fold) to the DNA-damaging agent mitomycin C and a very low spontaneous mutagenesis (reduced 100-fold). Adaptive laboratory evolution failed to restore cell fitness, except when coupled with a synthetic increase of the mutation rate, confirming low evolvability. Although mechanisms underlying this emergent phenotype are not understood, we propose that low evolvability can be leveraged in an engineering strategy coupling reductive cycles with evolutive cycles under induced mutagenesis., Nucleic Acids Research, 51 (6), ISSN:1362-4962, ISSN:0301-5610

Adherent-invasiveEscherichia coli(AIEC) strains are frequently recovered from stools of patients with dysbiotic microbiota. They have remarkable properties of adherence to the intestinal epithelium, and survive better than otherE. coliin macrophages. The best studied of these AIEC is probably strain LF82, which was isolated from a Crohn’s disease patient. This strain contains five complete prophages, which have not been studied until now. We undertook their analysis, bothin vitroand inside macrophages, and show that all of them form virions. The Gally prophage is by far the most active, generating spontaneously over 108viral particles per mL of culture supernatantsin vitro, more than 100-fold higher than the other phages. Gally is over-induced after a genotoxic stress generated by ciprofloxacin and trimethoprim. However, upon macrophage infection, Gally virion production is decreased by more than 20-fold, and the transcription profile of the prophage indicates that part of the structural module is specifically repressed while the replication module is overexpressed compared to unstressed culture conditions. We conclude that strain LF82 has evolved an efficient way to “tame” its most active prophage upon macrophage infection, which may participate to its good survival in macrophages. The results are discussed in light of the active lysogeny process.AUTHOR SUMMARYProphages are bacterial viruses stably integrated into their host, to which they can provide new functions, thus increasing their fitness in the environment. Thereby, they can participate to the virulence of bacterial pathogens. However, prophages are double-edged swords that can be awakened in response to genotoxic stresses, resulting in the death of their bacterial host. This raises the question of the effect of this type of stress in the natural environments where their bacterial hosts exert their virulence. In this study, we characterized the five active prophages present inEscherichia coliLF82, a strain belonging to the intestinal microbiota and suspected to be involved in Crohn’s disease via its ability to invade macrophages, a highly genotoxic environment. We show that LF82 inhibits the awakening of its prophages in macrophages, allowing it to survive there. Moreover, deletion of its most active prophage does not affect the viability of LF82 in this environment. These results show that LF82 has tamed its prophages in macrophages and also suggest that if they convey fitness advantages, they probably do so in environments differing from macrophages, and which remain to be discovered.

International audience; Double-strand breaks (DSBs) are the most detrimental DNA damage encountered by bacterial cells. DBSs can be repaired by homologous recombination thanks to the availability of an intact DNA template or by Non-Homologous End Joining (NHEJ) when no intact template is available. Bacterial NHEJ is performed by sets of proteins of growing complexity from Bacillus subtilis and Mycobacterium tuberculosis to Streptomyces and Sinorhizobium meliloti. Here, we discuss the contribution of these models to the understanding of the bacterial NHEJ repair mechanism as well as the involvement of NHEJ partners in other DNA repair pathways. The importance of NHEJ and of its complexity is discussed in the perspective of regulation through the biological cycle of the bacteria and in response to environmental stimuli. Finally, we consider the role of NHEJ in genome evolution, notably in horizontal gene transfer.

Enterococcus faecalis is an opportunistic pathogen that has emerged as a major cause of nosocomial infections worldwide. Many clinical strains are indeed resistant to last resort antibiotics and there is consequently a reawakening of interest in exploiting virulent phages to combat them. However, little is still known about phage receptors and phage resistance mechanisms in enterococci. We made use of a prophageless derivative of the well-known clinical strain E. faecalis V583 to isolate a virulent phage belonging to the Picovirinae subfamily and to the P68 genus that we named Idefix. Interestingly, most isolates of E. faecalis tested&mdash, including V583&mdash, were resistant to this phage and we investigated more deeply into phage resistance mechanisms. We found that E. faecalis V583 prophage 6 was particularly efficient in resisting Idefix infection thanks to a new abortive infection (Abi) mechanism, which we designated Abi&alpha, It corresponded to the Pfam domain family with unknown function DUF4393 and conferred a typical Abi phenotype by causing a premature lysis of infected E. faecalis. The abi&alpha, gene is widespread among prophages of enterococci and other Gram-positive bacteria. Furthermore, we identified two genes involved in the synthesis of the side chains of the surface rhamnopolysaccharide that are important for Idefix adsorption. Interestingly, mutants in these genes arose at a frequency of ~10&minus, 4 resistant mutants per generation, conferring a supplemental bacterial line of defense against Idefix.

International audience; Non-homologous end joining is a ligation process repairing DNA double strand breaks in eukaryotes and many prokaryotes. The ring structured eukaryotic Ku binds DNA ends and recruits other factors which can access DNA ends through the threading of Ku inward the DNA, making this protein a key ingredient for the scaffolding of the NHEJ machinery. However, this threading ability seems unevenly conserved among bacterial Ku. As bacterial Ku differ mainly by their C-terminus, we evaluate the role of this region in the loading and the threading abilities of Bacillus subtilis Ku and the stimulation of the DNA ligase LigD. We identify two distinct sub-regions: a ubiquitous minimal C-terminal region and a frequent basic C-terminal extension. We show that truncation of one or both of these sub-regions in Bacillus subtilis Ku impairs the stimulation of the LigD end joining activity in vitro. We further demonstrate that the minimal C-terminus is required for the Ku-LigD interaction, whereas the basic extension controls the threading and DNA bridging abilities of Ku. We propose that the Ku basic C-terminal extension increases the concentration of Ku near DNA ends, favoring the recruitment of LigD at the break, thanks to the minimal C-terminal sub-region.

Outside In Acquisition and analysis of large data sets promises to move us toward a greater understanding of the mechanisms by which biological systems are dynamically regulated to respond to external cues. Now, two papers explore the responses of a bacterium to changing nutritional conditions (see the Perspective by Chalancon et al. ). Nicolas et al. (p. 1103 ) measured transcriptional regulation for more than 100 different conditions. Greater amounts of antisense RNA were generated than expected and appeared to be produced by alternative RNA polymerase targeting subunits called sigma factors. One transition, from malate to glucose as the primary nutrient, was studied in more detail by Buescher et al. (p. 1099 ) who monitored RNA abundance, promoter activity in live cells, protein abundance, and absolute concentrations of intracellular and extracellular metabolites. In this case, the bacteria responded rapidly and largely without transcriptional changes to life on malate, but only slowly adapted to use glucose, a shift that required changes in nearly half the transcription network. These data offer an initial understanding of why certain regulatory strategies may be favored during evolution of dynamic control systems.

In March 1967 Chris Marker attended a screening of Loin du Vietnam (Far From Vietnam) in support of the long strike at the Rhodiaceta factory that year. From 1967 to 1977 Marker worked with the SLON collective, workers and other film‐makers both on militant films during the events of May 1968 and, equally importantly, on counter‐information films in solidarity with the struggle of the Third World revolutionary movements. These films, which do not separate political content from aesthetic enquiry, demonstrate Marker's aesthetic in which editing represents a political stake. By pushing back the limits of the language of film, rejecting a classical aesthetic and bringing about an encounter between the film‐maker and the filmed through the gaze, Chris Marker makes his work political.

SummaryDNA topoisomerases resolve DNA topological problems created during transcription, replication, and recombination. These ubiquitous enzymes are essential for cell viability and are highly potent targets for the development of antibacterial and antitumoral drugs. Type II enzymes catalyze the transfer of a DNA duplex through another one in an ATP-dependent mechanism. Because of its small size and sensitivity to antitumoral drugs, the archaeal DNA topoisomerase VI, a type II enzyme, is an excellent model for gaining further understanding of the organization and mechanism of these enzymes. We present the crystal structure of intact DNA topoisomerase VI bound to radicicol, an inhibitor of human topo II, and compare it to the conformation of the apo-protein as determined by small-angle X-ray scattering in solution. This structure, combined with a wealth of experimental data gathered on these enzymes, allows us to propose a structural model for the two-gate DNA transfer mechanism.

DNA polymerases of the X family have been implicated in a variety of DNA repair processes in eukaryotes. Here we show that Deinococcus radiodurans, a highly radioresistant bacterium able to mend hundreds of radiation-induced double-stranded DNA breaks, expresses a DNA polymerase belonging to the X family. This novel bacterial polymerase, named PolX(Dr), was identified as the product of the Deinococcal DR0467 gene. The purified PolX(Dr) protein possesses a DNA polymerase activity that is stimulated by MnCl2, a property of the X family DNA polymerases. Antibodies raised against PolX(Dr) recognized human pol lambda, rat pol beta and yeast Pol4 and, conversely, antibodies raised against these proteins recognized PolX(Dr). This immunological cross-reactivity suggests a high degree of structural conservation among the polymerases of the X family. Lack of PolX(Dr) reduced the rate of repair of double-stranded DNA breaks and increased cell sensitivity to gamma-rays. PolX(Dr) thus appears to play an important role in double-stranded DNA break repair in D. radiodurans.

International audience; Deinococcus radiodurans possesses an exceptional capacity to withstand the lethal and mutagenic effects of most form of DNA damage and has received considerable interest for use in both fundamental and applied research. Here we describe vectors that allow regulated expression of Deinococcal genes for functional analysis. The vectors contain the IPTG-regulated Spac system (Pspac promoter and lacI repressor gene), originally designed for Bacillus subtilis, that we have adapted to be functional in D. radiodurans. We show that the Spac system can control the expression of a lacZ reporter gene over two orders of magnitude depending on the inducer concentration and the copy number of the lacI regulatory gene. Furthermore, we demonstrate that the Spac system can be used to regulate the synthesis of a critical repair protein, such as RecA, resulting in a conditional mitomycin-resistant cell phenotype. We have also developed tools for the construction of conditional mutants where the expression of the target gene is regulated by an inducible promoter. The utility of these conditional gene inactivation systems is exemplified by the conditional lethal phenotype of a mutant expressing gyrA from the Pspac promoter.

International audience; Yeast Pus1p catalyzes the formation of pseudouridine (ψ) at specific sites of several tRNAs, but its function is not essential for cell viability. We show here that Pus1p becomes essential when another tRNA:pseudouridine synthase, Pus4p, or the essential minor tRNA for glutamine are mutated. Strikingly, this mutant tRNA, which carries a mismatch in the TψC arm, displays a nuclear export defect. Furthermore, nuclear export of at least one wild-type tRNA species becomes defective in the absence of Pus1p. Our data, thus, show that the modifications formed by Pus1p are essential when other aspects of tRNA biogenesis or function are compromised and suggest that impairment of nuclear tRNA export in the absence of Pus1p might contribute to this phenotype.

L'annee avec developpee le Japon la 1994 croissance. semble, a sur vu un l'ensemble enfin, rythme La reprise sortir vigoureux des economique de grands la recession. en pays Europe occidentaux s'est, Les Continentale, en pays particulier, renouer angloet avec la croissance. La reprise economique s'est, en particulier, developpee sur un rythme vigoureux en Europe Continentale, et le Japon semble, enfin, sortir de la recession. Les pay anglosaxons ont, quant a eux, connu une poursuite de la croissance forte de l'annee 1993. Cette conjoncture favorable s'est cependant deroulee dans un contexte de grands desequilibres epargne-investissement, que ce soit a l'echelon mondial ou au sein de chacun des pays. L'existence de soldes exterieurs tres eleves en valeur absolue au Japon (excedent) et aux Etats-Unis (deficit), ainsi que les besoins de financement considerables des gouvernements, continuent d'influencer profondement les comportements d'epargne et l'allocation de celle-ci.

In prokaryotes, transcription results from the activity of a 400 kDa RNA polymerase (RNAP) protein complex composed of at least five subunits (2 alpha, beta, beta', omega). To ensure adequate responses to changing environmental cues, RNAP activity is tightly controlled by means of interacting regulatory proteins. Here, we report the affinity-purification of the Bacillus subtilis RNAP complexes from cells in different growth states and stress conditions, and the quantitative assessment by mass spectrometry of the dynamic changes in the composition of the RNAP complex. The stoichiometry of RNA polymerase was determined by a comparison of two mass spectrometry-based quantification methods: a label-based and a label-free method. The validated label-free method was then used to quantify the proteins associated with RNAP. The levels of sigma factors bound to RNAP varied during growth and exposure to stress. Elongation factors, helicases such as HelD and PcrA, and novel unknown proteins were also associated with RNAP complexes. The content in 6S RNAs of purified RNAP complexes increased at the onset of the stationary phase. These quantitative variations in the protein and RNA composition of the RNAP complexes well correlate with the known physiology of B. subtilis cells under different conditions.

Der Verlauf der Konjunkturzyklen in den Vereinigten Staaten. Eine herkömmliche dynamische Modellbildung, von Patrick Artus, François Lecointe. In den Vereinigten Staaten ist der "normale" Verlauf eines Konjunkturzyklus in jüngster Zeit Gegenstand zahlreicher Diskussionen gewesen. Nachdem untersucht worden ist, welche Verhaltensweisen oder Mechanismen zyklische Schwankungen verursachen können, wird in diesem Artikel ein dynamisches Ökonomerriemodell für die amerikanische Wirtschaft geschätzt. Dies ermöglicht es, die Dauer, die Periodizität und die Ursache der amerikanischen Konjunkturzyklen zu bestimmen, und gibt Aufschluß über die Diskussionen, die gegenwärtig tiber die Möglichkeit der Überwindung der Rezession geführt werden., What is the Configuration of Cycles in the United States? A Traditional Dynamic Model, by Patrick Artus, François Lecointe. The "normal"confïguration of economic cycles has recently been under review in the United States. After examination of the behaviours or mechanisms causing cyclical fluctuations, we have derived a dynamic econometric model for the American economy. This makes it possible to determine the scope, periodicity and sources of American economic cycles, and thus to clarify current debate on what emergence from recession will be like., Quelle est la configuration des cycles aux États-Unis ? Une modélisation dynamique traditionnelle, par Patrick Artus, François Lecointe. La configuration "normale" d'un cycle économique a fait récemment l'objet de nombreuses interrogations aux États-Unis. Après avoir examiné quels comportements ou mécanismes pouvaient être à l'origine de fluctuations cycliques, nous estimons un modèle économétrique dynamique pour l'économie américaine. Cela permet de déterminer l'ampleur, la périodicité et la source des cycles économiques américains, et ainsi d'éclairer les débats présents sur le profil de sortie de récession., Configuración de los ciclos económicos en los Estados Unidos. Modelización dinámica conventional, por Patrick Artus y François Lecointe. La configuración "normal" de un ciclo económico fue sometida recientemente a un análisis en los Estados Unidos. Tras examinar los comportamientos o los mecanismos que pueden originar fluctuaciones cîclicas, se élabora un modelo econométrico dinámico para la economía estadounidense. Esto permite determinar la importancia, la periodicidad y la fuente de los ciclos económicos estadounidenses y aclarar así los debates actuales respecto a las soluciones que permitan salir de la recesión., Artus Patrick, Lecointe François. Quelle est la configuration des cycles aux États-Unis ? Une modélisation dynamique traditionnelle. In: Économie & prévision, n°107, 1993-1. Études internationales. pp. 1-14.

Patrick Artus et François Lecointe Financial crises and private indebtedness crisis in the United-States. The recession in the United-States focused attention on private agents overindebtedness and on the fragility of the financial system. In light of recent works, it seems that a cyclical slowdown has more damaging consequences on an economy where agents are heavily indebted where the banking system is disordered. Following the inverse causality, the actual slowdown maybe attributed to the fragility of the financial system. In turn, the banking crisis the United-States is confronted to, is nor only a consequence of réglementation and excessive competitiveness, but also of over ten years of assets underpricing, a less mentionned fact. In the case households, the growth of their assets and debt weakens their financial situation. For non-financial companies empirical evidence shows that a rise in their indebtedness increases their failure rate, which is not necessarily true from a theoretical point of view., Patrick Artus et François Lecointe Crise financière et crise de l'endettement privé aux Etats-Unis. La recession de l'économie américaine pose de façon aiguë la question du surendettement des agents économiques et de la fragilité du système financier des Etats-Unis. A la lumière des travaux les plus récents, il apparaît qu'un ralentissement cyclique de l'activité a des conséquences plus graves sur une économie dont les agents sont fortement endettés et dont le système bancaire est fragilisé. Suivant une causalité inverse, l'actuel ralentissement peut être partiellement imputé à la situation de fragilité financière. Mais la crise bancaire à laquelle font face les Etats-Unis tient plus à des causes autonomes : l'inadaptation de la réglementation et la concurrence excessive, mais aussi — et ce fait est moins signalé — la fixation de prix irréalistes pour les actifs financiers depuis dix ans. Dans le cas des ménages, la croissance simultanée de leurs actifs et de leurs dettes conduit en fait à une fragilisation de leur situation. Enfin, il apparaît empiriquement qu'une hausse de l'endettement fragilise les entreprises et accroît leur taux de défaillance, ce qui n'est pas évident a priori d'un point de vue théorique ; il reste que la progression des faillites dans la décennie quatre-vingt provient plus des politiques monétaires restrictives., Artus Patrick, Lecointe François. Crise financiére et crise de l'endettement privé aux Etats-Unis. In: Revue française d'économie, volume 6, n°1, 1991. pp. 37-85.

Mimosa, a macroeconomic model of the world economy, jointly built by the CEPII and the OFCE, is now operational. This article presents its main features and describes some monetary and fiscal multipliers. The economies of the six bigger industrialised countries are described in great detail by neo-keynesian models : a five product disaggregation distinguishes the energy sector, agriculture, the non-traded sector, the government sector and the industrial sector for which a putty-clay production function ensures compatibilities between employment, investment and production capacity behaviour. These models allow a precise analysis of the consequences of many kinds of monetary or fiscal policies. The rest of the world is divided into nine zones, more succinctly modelled : the model reveals in particular the financing constraints which bear on the imports of the less developed countries. International trade is analysed through a four product disaggregation. The article shows the model's properties while describing the impacts, in the country and abroad, of an increase in public expenditure in one of the major countries. It studies the consequences of a decline of the value of the dollar and finally the implications of a woldwide decrease in interest rates. Although it remains, in some respects, work in progress, the Mimosa model is already a useful tool for understanding the functioning of the world economy and for predicting its evolution., MIMOSA, modèle macroéconomique de l'économie mondiale, construit en commun par le CEPII et l'OFCE est maintenant opérationnel. Le présent article en présente les principales caractéristiques ainsi que quelques propriétés variantielles. Les économies des six plus importants pays industrialisés sont décrites en détail par des modèles d'inspiration néo-keynésienne ; le découpage en cinq branches permet d'isoler l'énergie, le secteur agricole, le secteur abrité, le secteur non-marchand et l'industrie où la fonction de production, de type putty-clay, permet d'assurer la cohérence des comportements d'emploi, d'investissement, d'accumulation de capacités de production. Ces modèles autorisent une analyse fine des diverses mesures de politiques budgétaires ou monétaires. Neufs zones, analysées plus sommairement, regroupent le reste du monde : le modèle intègre en particulier les contraintes de financement qui pèsent sur les possibilités d'importations des pays en développement. Les interdépendances commerciales sont décrites en quatre produits. L'article analyse comment le modèle rend compte des effets différenciés sur l'économie considérée et sur l'économie mondiale d'une hausse des dépenses publiques survenant dans un des grands pays. Il étudie ensuite les conséquences d'une baisse du dollar, puis d'une baisse généralisée des taux d'intérêt. Bien qu'il reste, à certains égards, en construction, le modèle MIMOSA constitue déjà un outil utile pour comprendre le fonctionnement de l'économie mondiale et prévoir son évolution., Equipe MIMOSA, Pisani-Ferry Jean, Sterdyniak Henri, CEPII, OFCE, Blonde Marie-Hélène, Coudert Virginie, Delessy Henri, Fiole Murielle, Harasty Hélène, Henry Jérôme, Le Dem Jean, Paris-Horvitz Sébastien, Avouyi-Dovi Sanvi, Lecointe François, Kremp Elizabeth, Charpin Françoise, Frochen Patrick, Gaye Pierre, Topol Richard, Giraud Christian, Nowocien Romuald. MIMOSA, une modélisation de l'économie mondiale. In: Observations et diagnostics économiques : revue de l'OFCE, n°30, 1990. pp. 137-197.

Hystereseauswirkungen auf den amerikanischen Aussenhandel, von Philippe Ducos, François Lecointe. Dieser Artikel geht von der Feststellung aus, dass das amerikanische Aussenhandelsdefizit noch immer nicht ausgegli.chen ist, nachdem Anfang 1987 der Dollar zur Parität zurückgekehrt war, die zu Beginn der achtziger Jahre galt, und schlägt einen Überblick über die letzten Modelle des Aussenhandels vor, die die Remanenz der Auswirkungen zu erklären vermögen, die sich aus der Höherbewertung der amerikanischen Devise ergeben haben. Durch ökonometrische Tests können dièse Hysterese-Modelle sodann bestätigt werden. Gleichwohl wird gezeigt, dass die Desaggregationsebene der Produkte mit höchstmöglicher Genauigkert bestimmt werden muss ; es ist offensichtlich, dass die Höherbewertung des Dollars während der Jahre 1981/85 weiterhin nachteilige Folgen in zwei Sektoren hat : in dem der langlebigen Konsumgüter und in dem der Investitionsgüter. Die beiden wichtigen Kategorien theoretischer Modelle (Einfuhrkosten, Nachfragedynamik) sind in Betracht zu ziehen., Hysteresis effects on US external trade, by Philippe Ducos, François Lecointe. In spite of a declining dollar and a return to its 1980 parity in 1987, the US trade deficit has not been eliminated yet. This paper surveys recent trade models which explain hysteresis effects on external trade and presents empirical evidence. It is shown that the use of disaggregated data is crucial to validate the models. It seems that the dollar appreciation has changed the market structure of both the consumer durable goods sector and the capital goods sector. The corresponding theoretical models would be the sunk cost model and demand dynamics model respectively., Effets d'hystérésis sur le commerce extérieur américain, par Philippe Ducos, François Lecointe. Partant du constat que le déficit extérieur américain ne s'est toujours pas résorbé après le retour du dollar, début 1987, à sa parité du début des années quatre-vingt, cet article propose une revue des modèles récents de commerce extérieur qui permettent d'expljquer la rémanence des effets de la forte appréciation de la devise américaine. Des tests économétriques permettent ensuite de valider ces modèles d'hystérésis. On montre toutefois qu'il est nécessaire de se placer à un niveau de désagrégation des produits suffisamment fin ; il apparaît que l'appréciation du dollar des années 1981/1985 continue d'avoir des conséquences dommageables dans deux secteurs : celui des biens de consommation durables et celui des biens d'équipement, les deux grands types de modèles théoriques (coût d'entrée, dynamique de la demande) étant envisageables., Efectos de histérisis en el comercio exterior norteamericano, por Philippe Ducos y François Lecointe. Teniendo en cuenta que no se ha logrado enjugar el déficit exterior norteamericano, pese a que el dólar recobró a comienzos de 1987 la misma paridad que tenîa a comienzos de los años ochenta, este artículo propone un análisis de los modelos recientes de comercio exterior que permiten explicar la persistence de los efectos de la gran apreciación de la divisa estadounidense. Los tests econométricos permiten validar estos modelos de histéresis. No obstante se demuestra que es necesario situarse en un nivel suficientemente preciso de desagregación de los productos. De esta forma puede observarse que la apreciación del dólar de los años 1981/1985 sigue teniendo consecuencias perjudiciables en dos sectores, el de los bienes de consumo duraderos y el de los bienes de equipo, pudiéndose considerar los dos principales tipos de modelos teóricos (coste de entrada, dinámica de la demanda)., Ducos Philippe, Lecointe François. Effets d'hystérésis sur le commerce extérieur américain. In: Économie & prévision, n°94-95, 1990-3-4. Aspects de la contrainte extérieure. pp. 79-93.

International audience; In bacteria, several salvage responses to DNA replication arrest culminate in reassembly of the replisome on inactivated forks to resume replication. The PriA DNA helicase is a prominent trigger of this replication restart process, preceded in many cases by a repair and/or remodeling of the arrested fork, which can be performed by many specific proteins. The mechanisms that target these rescue effectors to damaged forks in the cell are unknown. We report that the single‐stranded DNA binding (SSB) protein is the key factor that links PriA to active chromosomal replication forks in vivo. This targeting mechanism determines the efficiency by which PriA reaches its specific DNA‐binding site in vitro and directs replication restart in vivo. The RecG and RecQ DNA helicases, which are involved in intricate replication reactivation pathways, also associate with the chromosomal replication forks by similarly interacting with SSB. These results identify SSB as a platform for linking a ‘repair toolbox’ with active replication forks, providing a first line of rescue responses to accidental arrest.

International audience; To evaluate the importance of RecA in DNA double‐strand break (DSB) repair, we examined the effect of low and high RecA concentrations such as 2500 and 100 000 molecules per cell expressed from the inducible Pspac promoter in Deinococcus radiodurans in absence or in presence of IPTG respectively. We showed that at low concentration, RecA has a negligible effect on cell survival after γ‐irradiation when bacteria were immediately plated on TGY agar whereas it significantly decreased the survival to γ‐irradiation of ΔddrA cells while overexpression of RecA can partially compensate the loss of DdrA protein. In contrast, when cells expressing limited concentration of RecA were allowed to recover in TGY2X liquid medium, they showed a delay in mending DSB, failed to reinitiate DNA replication and were committed to die during incubation. A deletion of irrE resulted in sensitivity to γ‐irradiation and mitomycin C treatment. Interestingly, constitutive high expression of RecA compensates partially the ΔirrE sensitization to mitomycin C. The cells with low RecA content also failed to cleave LexA after DNA damage. However, neither a deletion of the lexA gene nor the expression of a non‐cleavable LexA(Ind–) mutant protein had an effect on survival or kinetics of DNA DSB repair compared with their lexA+ counterparts in recA+ as well as in bacteria expressing limiting concentration of RecA, suggesting an absence of relationship between the absence of LexA cleavage and the loss of viability or the delay in the kinetics of DSB repair. Thus, LexA protein seems to play no major role in the recovery processes after γ‐irradiation in D. radiodurans.

International audience; Interactions between dendritic cells and Mycobacterium tuberculosis, the aetiological agent of tuberculosis in humans, are thought to be central to anti-mycobacterial immunity. We have previously shown that M. tuberculosis binds to human monocyte-derived dendritic cells mostly through the C-type lectin DC-SIGN (dendritic-cell-specific intercellular molecule-3-grabbing non-integrin)/CD209, and we have suggested that DC-SIGN may discriminate between mycobacterial species through recognition of the mannose-capping residues on the lipoglycan lipoarabinomannan of the bacterial envelope. Here, using a variety of fast- and slow-growing Mycobacterium species, we provide further evidence that mycobacteria recognition by DC-SIGN may be restricted to species of the M. tuberculosis complex. Fine analyses of the lipoarabinomannan molecules purified from these species show that the structure and amount of these molecules alone cannot account for such a preferential recognition. We propose that M. tuberculosis recognition by DC-SIGN relies on both a potential difference of accessibility of lipoarabinomannan in its envelope and, more probably, on the binding of additional ligands, possibly including lipomannan, mannose-capped arabinomannan, as well as the mannosylated 19 kDa and 45 kDa [Apa (alanine/proline-rich antigen)] glycoproteins. Altogether, our results reveal that the molecular basis of M. tuberculosis binding to DC-SIGN is more complicated than previously thought and provides further insight into the mechanisms of M. tuberculosis recognition by the immune system.

International audience; Many different modified nucleotides are found in naturally occurring tRNA, especially in the anticodon region. Their importance for the efficiency of the translational process begins to be well documented. Here we have analyzed the in vivo effect of deleting genes coding for yeast tRNA-modifying enzymes, namely Pus1p, Pus3p, Pus4p, or Trm4p, on termination readthrough and +1 frameshift events. To this end, we have transformed each of the yeast deletion strains with a lacZ-luc dual-reporter vector harboring selected programmed recoding sites. We have found that only deletion of the PUS3 gene, encoding the enzyme that introduces pseudouridines at position 38 or 39 in tRNA, has an effect on the efficiency of the translation process. In this mutant, we have observed a reduced readthrough efficiency of each stop codon by natural nonsense suppressor tRNAs. This effect is solely due to the absence of pseudouridine 38 or 39 in tRNA because the inactive mutant protein Pus3[D151A]p did not restore the level of natural readthrough. Our results also show that absence of pseudouridine 39 in the slippery tRNA(UAG)(Leu) reduces +1 frameshift efficiency. Therefore, the presence of pseudouridine 38 or 39 in the tRNA anticodon arm enhances misreading of certain codons by natural nonsense tRNAs as well as promotes frameshifting on slippery sequences in yeast.

International audience; The genome of Saccharomyces cerevisiae encodes three close homologues of the Escherichia coli 2′‐O‐rRNA methyltransferase FtsJ/RrmJ, designated Trm7p, Spb1p and Mrm2p. We present evidence that Trm7p methylates the 2′‐O‐ribose of nucleotides at positions 32 and 34 of the tRNA anticodon loop, both in vivo and in vitro. In a trm7Δ strain, which is viable but grows slowly, translation is impaired, thus indicating that these tRNA modifications could be important for translation efficiency. We discuss the emergence of a family of three 2′‐O‐RNA methyltransferases in Eukaryota and one in Prokaryota from a common ancestor. We propose that each eukaryotic enzyme is located in a different cell compartment, in which it would methylate a different RNA that can adopt a very similar secondary structure.

The enzymatic activity of yeast gene product Deg1 was identified using both disrupted yeast strain and cloned recombinant protein expressed in yeast and in Escherichia coli. The results show that the DEG1-disrupted yeast strain lacks synthase activity for the formation of pseudouridines psi 38 and psi 39 in tRNA whereas the other activities, specific for psi formation at positions 13, 27, 28, 32, 34, 35, 36, and 55 in tRNA, remain unaffected. Also, the His6-tagged recombinant yeast Deg1p expressed in E. coli as well as a protein fusion with protein A in yeast display the enzymatic activity only toward psi 38 and psi 39 formation in different tRNA substrates. Therefore, Deg1p is the third tRNA:pseudouridine synthase (Pus3p) characterized so far in yeast. Disruption of the DEG1 gene is not lethal but reduces considerably the yeast growth rate, especially at an elevated temperature (37 degrees C). Deg1p localizes both in the nucleus and in the cytoplasm, as shown by immunofluorescence microscopy. Identification of the pseudouridine residues present (or absent) in selected naturally occurring cytoplasmic and mitochondrial tRNAs from DEG1-disrupted strain points out a common origin of psi 38- and psi 39-synthesizing activity in both of these two cellular compartments. The sensitivity of Pus3p (Deg1p) activity to overall three-dimensional tRNA architecture and to a few individual mutations in tRNA was also studied. The results indicate the existence of subtle differences in the tRNA recognition by yeast Pus3p and by its homologous tRNA:pseudouridine synthase truA from E. coli (initially called hisT or PSU-I gene product).

New indicators of effective exchange rates were published in the November issue of the OFCE monthly newsletter; this will be continued on a regular basis. The purpose of this note is to state the methods used to build these indicators and to present a selection of the series calculated and available at OFCE., Des indicateurs de taux de change effectifs ont été publiés dans la Lettre de l'OFCE de novembre 1988 et le seront désormais périodiquement. La présente note a pour but d'en préciser les méthodes de construction et de fournir une sélection des séries calculées et disponibles à l'OFCE., Le Cacheux Jacques, Lecointe François. Les taux de change effectifs des grandes devises. In: Observations et diagnostics économiques : revue de l'OFCE, n°26, 1989. pp. 189-196.

Whereas the seventies' had been characterized by major changes in the relative prices of goods and services, the rise in real interest rates, from 1980 on, has initiated an era of turmoil in the financial markets. The various relative price shocks — the oil price hikes, the rising real interest rates, the dollar appreciating vis-à-vis European currencies — have generally had negative consequences on production costs and demand. Their analysis requires combining supply and demand considerations, together with the interactions between financial markets and activity. The worldwide increase of real interest rates may be attributed first to restrictive monetary policy in the United States, then to increased profitability of investment in this country. The swelling federal budget deficit cannot, on its own, explain such a worldwide increase in real rates, in so far as fiscal policies in the rest of the world have been much tighter ; but it has contributed to the persistance a significant differential between US rates and those in the rest of the world. Worldwide high real interest rates have made the latest recession atypical. Indeed their effects both on the stock of productive capital and on firms' management of personnel have induced substantial increases in productivity at an early stage of the cycle. In most countries, productivity increases, together with the usual moderating effects on wages of slack in the labor markets, have been sufficient to rapidly cancel the rise in the share of wages in value added that had taken place in the seventies'. Such a restoration of firms' profit conditions may explain the persistance of higher real interest rates than what would be warranted by recent monetary and fiscal policies., Alors que les modifications importantes de prix relatifs dans les années soixante-dix ont essentiellement concerné les biens et services, la hausse des taux d'intérêt réels à partir de 1980 inaugure une phase de bouleversements des prix sur les marchés financiers. Ces chocs de prix relatifs — hausse du prix des produits pétroliers, accroissement des taux d'intérêt réels, appréciation du dollar pour les pays européens — ont eu dans l'ensemble des conséquences néfastes sur les coûts de production et sur les débouchés, dont l'analyse requiert une approche articulant aspects d'offre et de demande d'un côté, interactions entre marchés de capitaux et activité productive de l'autre. La hausse des taux d'intérêt réels mondiaux peut être attribuée dans un premier temps à la politique monétaire restrictive menée aux Etats-Unis, puis à l'augmentation de la rentabilité de l'investissement dans ce pays. Le creusement du déficit budgétaire américain ne permet pas, quant à lui, d'expliquer la hausse mondiale des taux réels, dans la mesure où il s'est accompagné de politiques budgétaires plus restrictives dans le reste du monde ; mais il contribue au maintien d'un différentiel entre les taux américains et ceux du reste du monde. Le niveau élevé des taux réels mondiaux est à l'origine de la spécificité de la dernière récession. Elle a en effet rapidement conduit à des gains de productivité conséquents, par ses effets simultanés sur le stock de capital productif et sur la gestion du personnel des entreprises. Ces gains, alliés aux conséquences habituelles sur les salaires de la détérioration de l'emploi, ont été, dans la plupart des pays, d'une ampleur telle que l'accroissement de la part salariale au cours des années soixante-dix a été effacé en quelques années. Cette restauration des profits des entreprises est de nature à expliquer le maintien d'un niveau élevé des taux d'intérêt réels bien au-delà de ce que justifieraient les politiques monétaires et budgétaires nationales., Fitoussi Jean-Paul, Le Cacheux Jacques, Lecointe François, Vasseur Christian. Taux d'intérêt réels et activité économique. Un essai d'interprétation théorique et de mesure empirique. In: Observations et diagnostics économiques : revue de l'OFCE, n°15, 1986. pp. 145-173.

Real Exchange Rates and Competitiveness : France, Italy, the FRG and the USA Jacques Le Cacheux, François Lecointe The study of an economy's international competitiveness is notoriously difficult, in that it has to simultaneously take account of factors that can be regarded as exogenous to the firm — such as exchange rates and production costs — and of aspects that result from the firm's behavior — their mark-up rates and their desired market shares in particular. The nominal evolutions observed in recent years have been too diverse to allow any immediate inference of possible modifications in relative competitive positions. This paper presents a simple modelling of price determination on imperfectly competitive and geographically distinct markets, a characterization that seems to fit the actual trade of many manufactured goods. In such a framework firms react to variations in their costs or in the exchange rates both by altering their mark-up and by witnessing gains or losses in their market shares. A new indicator of the real effective exchange rates of the US dollar, the French Franc, the Deutsche Mark and the Italian Lira is also presented and discussed. Comparing it with several commonly used indicators leads to a more nuanced judgement about real movements of these currencies in recent years. Eventually a tentative reading of the changing market shares in the US and of the trend in the ratio of exports to imports of manufactured goods for these countries is proposed in the light of observed evolutions in various complementary measures of competitiveness. This last exercise reveals the power, but also the limitations, of the approach., L'étude de la compétitivité internationale d'une économie est notoirement délicate, en ce qu'elle doit prendre en considération à la fois des éléments que l'on peut considérer comme exogènes à l'entreprise — tels que les taux de change et les coûts de production — et, dans une certaine mesure, des aspects qui résultent de leurs comportements — la fixation de leurs marges et leurs objectifs de parts de marché en particulier. Les évolutions nominales observées depuis quelques années sont trop disparates pour que l'on puisse en induire les modifications des positions concurrentielles. Cet article propose une formalisation simple de la détermination des prix sur des marchés imparfaitement concurrentiels et géographiquement cloisonnés, caractéristiques qui semblent correspondre aux échanges commerciaux de bon nombre de produits manufacturés. Dans ce cadre d'hypothèses les entreprises réagissent aux variations de coûts ou de change à la fois en modifiant leurs marges et en enregistrant des gains ou pertes de parts de marché. Par ailleurs cette étude présente un nouvel indicateur du taux de change effectif réel du dollar et de trois grandes monnaies européennes, le franc, le mark et la lire. La comparaison de cet indicateur avec ceux qui sont couramment utilisés conduit à moduler sensiblement le jugement porté sur les mouvements réels de ces monnaies. Enfin la mise en parallèle des évolutions de plusieurs mesures complémentaires des positions concurrentielles et des modifications du partage du marché américain et des taux de couverture manufacturiers des pays étudiés révèle l'intérêt, mais aussi les limites, de la démarche adoptée., Le Cacheux Jacques, Lecointe François. Changes réels et compétitivité de la France, l'Italie, la RFA et les Etats-Unis. In: Observations et diagnostics économiques : revue de l'OFCE, n°20, 1987. pp. 149-187.