Conformational changes of a Swi2/Snf2 ATPase during its mechano-chemical cycle

Remodelling protein nucleic acid interfaces is an important biological task, which is often carried out by nucleic acid stimulated ATPases of the Swi2/Snf2 superfamily. Here we study the mechano-chemical cycle of such an ATPase, namely the catalytic domain of the Sulfolobus solfataricus Rad54 homologue (SsoRad54cd), by means of fluorescence resonance energy transfer (FRET). The results of the FRET studies show that the enzyme can be found in (at least) two different possible conformations in solution. An open conformation, consistent with a recently reported crystal structure, is converted into a closed conformation after DNA binding. Upon subsequent binding of ATP no further change in conformation can be detected by the FRET measurements. Instead, a FRET detectable conformational change occurs after ATP hydrolysis and prior to ADP release, suggesting a powerstroke that is linked to phosphate release. Based on these data we will present a new model for the mechano-chemical cycle of this enzyme. This scheme in turn provides a working model for understanding the function of other members of the Swi2/Snf2 family

Dual FRET assay for detecting receptor protein interaction with DNA

We present here a new assay that is based on the idea of the molecular beacon. This assay makes it possible to investigate two proteins interacting with DNA at two binding sites that are close to each other. The effectiveness of the test depends on the exclusive binding of three DNA fragments in the presence of two proteins, and the monitoring of the process depends upon observing the quenching of two independent fluorescence donors. As a model we used the components of the heterodimeric ecdysteroid receptor proteins ultraspiracle (Usp) and ecdysone receptor (EcR) from Drosophila melanogaster and a response element from the promoter of the hsp27 gene. The response element consists of two binding sites (half-sites) for the DNA binding domains (DBDs). We have shown that protein–protein interactions mediate cooperative binding of the ecdysteroid receptor DBDs to a hsp27pal response element. The analysis of the microscopic dissociation constants obtained with the DMB led to the conclusion that there was increased affinity of UspDBD to the 5′ half-site in the presence of EcRDBD when the 3′ half-site was occupied, and increased affinity of EcRDBD to the 3′ half-site when the 5′ half-site was occupied

Initial Phase of Photoelectrochemical Conditioning of Silicon in Alkaline Media: Surface Chemistry and Topography

Oxidation and dissolution phenomena of Si(111) in alkaline electrolyte are investigated by a combination of photoelectrochemistry, scanning probe microscopy (SPM), transmission electron microscopy (TEM) and in-system synchrotron radiation photoelectron spectroscopy (SRPES). The surface topography in the initial anodic potential regime shows the formation of mesoscale pores with widths in the range 300–500 nm and partial surface oxidation. The surface chemistry assessment by SRPES shows patchy silicon oxide growth, suboxides, and remnants of the former hydrogen terminated surface areas. The use of the obtained self-organized nanostructures for application in nanoemitter photocatalytic solar cells is discussed. The necessary requirements regarding the total surface area of electrocatalysts needed to sustain the current density due to light-induced excess minority carriers in conjunction with the exchange current density of the considered heterogeneous catalysts is discussed

L’Afrique subsaharienne à l’épreuve de la crise

Sub-Saharan Africa towards the Crisis. Sub-Saharan African countries are still less integrated into global financial markets than emerging economies. However, spillover effects from global crisis after the Lehman Brothers bankruptcy in 2008 also hit African economies. The international trade collapse and the downturn of foreign capital inflows led to a major growth slowdown in 2009 ; this slowdown differed according to African countries’ exposure to the globalization. The implementation of countercyclical budgetary policies certainly provided support for economic activities but resulted in higher fiscal deficit and public indebtedness. The decline of international trade weakened current accounts of many Sub-Saharan African countries ; however, no specific tensionMême s’ils sont moins intégrés à l’économie mondiale que les pays émergents, les pays d’Afrique sub-saharienne ont subi les conséquences de la crise mondiale qui a éclaté avec la chute de Lehman Brothers en 2008. La baisse de la demande mondiale et la contraction des flux de capitaux internationaux ont entraîné une perte de croissance significative mais très hétérogène au sein du continent. Dans certains cas, les politiques budgétaires volontaristes ont permis de contenir le ralentissement mais en raison d’une forte contraction des recettes, ces politiques ont également provoqué un creusement significatif des déficits publics. Parallèlement, le recul du commerce mondial a fortement dégradé les soldes courants de certains pays sans toutefois générer une chute généralisée de la liquidité externe. Dans une perspective de moyen terme, l’impact de la crise internationale révèle la nécessité de renforcer les outils de pilotage de la politique macroéconomique pour réagir aux chocs externes (politiques monétaire et budgétaire). À plus long terme, cette crise appelle le développement de politiques économiques actives susceptibles d’appuyer la mobilisation des ressources intérieures (fiscalité, secteur financier), le renforcement de la compétitivité (diversification productive, accords commerciaux...) et le développement de politiques sociales efficaces. Classification JEL : G01, F30, O57.Bedossa Bastien, Bellocq François-Xavier, Jacquet, Letilly Gäelle. L’Afrique subsaharienne à l’épreuve de la crise. In: Revue d'économie financière, n°100, 2010. Le risque systémique 1. Repenser la finance. pp. 89-107

Characteristics and performance improvement of anode supported solid oxide fuel cells based on BaIn(0.)3Ti(0.7)O(2.85) (BIT07) as electrolyte, BIT07-Ni as anode and La(0.58)Sr(0.4)Co(0.2)Fe(0.8)O(3-delta) (LSCF) as cathode

International audienceThis study deals with the electrochemical performance of anode supported solid oxide fuel cells (SOFCs) based on perovskite-type materials: BaIn0.3Ti0.7O2.85 (BIT07) as electrolyte, BIT07-Ni as a cermet anode and La0.58Sr0.4Co0.2Fe0.8O3−δ (LSCF) as cathode. Anode/electrolyte assemblies have been realised by tape casting and co-firing and the cathode has been deposited by screen-printing. The performance of BIT07-Ni/BIT07/LSCF cells has been determined at 700 °C under humidified (3% H2O) hydrogen as fuel and air as oxidant. Two cells, with different electrolyte thicknesses: 23 and 11 μm, have been tested and they exhibited power densities at 0.7 V around 209 and 336 mW cm−2, respectively. Electrochemical Impedance Spectroscopy (EIS) measurements have also been carried out and allowed to differentiate between the series and polarisation resistances

Performances commerciales de l'Afrique subsaharienne : une diversification nécessaire

(English) This study analyses trade strategies and performances of a sample of seven Sub-Saharan African countries (South Africa, Côte d’Ivoire, Ghana, Madagascar, Mauritius, Nigeria and Senegal), which together represent over two-thirds of Africa’s total exports. Although the poor overall Africa’s trade performance can be explained to a great extent by well known factors (commodity prices, macroeconomic problems, etc.), this does nothing to explain why some countries succeed to increase their exports and not others. This paper attempts to do so, by splitting these countries’ export growth rate during the 1990s, into a demand effect and a competitiveness effect. This allows us to appreciate the impact of specialization on trade performance: if a country is specialised in goods for which there is little world demand, or whose sales prices are falling, its exports will be affected accordingly. According to this breakdown, it is not trade specialisation that explains why certain countries succeeded, but above all their competitiveness, that is their ability to increase their market shares on both traditional and new export products. The analysis also clearly shows that the best performing countries are precisely those which have diversified their exports the most, such as Madagascar (thanks to its export processing zones), South Africa and Ghana. _________________________________ (français) Cette étude analyse les stratégies et les performances commerciales de sept pays d’Afrique subsaharienne (Afrique du Sud, Côte d’Ivoire, Ghana, Madagascar, Maurice, Nigeria et Sénégal) durant les années 1990. Ces pays représentent plus des deux tiers des exportations totales africaines. Bien que les médiocres performances globales de l’Afrique en général puissent être attribuées en grande partie à des facteurs bien connus (baisse du prix des matières premières, problèmes macroéconomiques, etc.), ceci n’explique pas pourquoi certains pays arrivent à accroître leurs exportations et d’autres non. Pour répondre à cette question, on procède à une décomposition comptable de la croissance des exportations de chaque pays entre un effet spécialisation sectorielle et un effet de compétitivité. Le premier effet permet d’évaluer par exemple l’impact d’une baisse des prix ou de la demande pour les secteur s dans lesquels un pays est spécialisé ; le second effet mesure les gains/pertes de parts de marché au niveau de chaque produit traditionnellement ou nouvellement exporté. Cette décomposition montre que les écarts de performances entre pays ne s’expliquent pas par les différences de spécia lisation mais par celles de compétitivité. De manière cohérente, l’analyse menée en termes d’indices de diversification montre que les pays les plus performants sont ceux qui ont réussi à diversifier le plus leurs exportations, à savoir Madagascar (à travers l’essor de ses zones franches), l’Afrique du Sud et le Ghana.

Mise en forme et évaluation des performances de cellules de piles à combustible SOFC à base de Baln 0,3 TI0,7 O2,85 (BIT07)

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