Probing the (H3-H4)(2) histone tetramer structure using pulsed EPR spectroscopy combined with site-directed spin labelling

The (H3-H4)2 histone tetramer forms the central core of nucleosomes and, as such, plays a prominent role in assembly, disassembly and positioning of nucleosomes. Despite its fundamental role in chromatin, the tetramer has received little structural investigation. Here, through the use of pulsed electron-electron double resonance spectroscopy coupled with site-directed spin labelling, we survey the structure of the tetramer in solution. We find that tetramer is structurally more heterogeneous on its own than when sequestered in the octamer or nucleosome. In particular, while the central region including the H3-H3′ interface retains a structure similar to that observed in nucleosomes, other regions such as the H3 αN helix display increased structural heterogeneity. Flexibility of the H3 αN helix in the free tetramer also illustrates the potential for post-translational modifications to alter the structure of this region and mediate interactions with histone chaperones. The approach described here promises to prove a powerful system for investigating the structure of additional assemblies of histones with other important factors in chromatin assembly/fluidity

The histone chaperones Nap1 and Vps75 bind histones H3 and H4 in a tetrameric conformation

Histone chaperones physically interact with histones to direct proper assembly and disassembly of nucleosomes regulating diverse nuclear processes such as DNA replication, promoter remodeling, transcription elongation, DNA damage, and histone variant exchange. Currently, the best-characterized chaperone-histone interaction is that between the ubiquitous chaperone Asf1 and a dimer of H3 and H4. Nucleosome assembly proteins (Nap proteins) represent a distinct class of histone chaperone. Using pulsed electron double resonance (PELDOR) measurements and protein crosslinking, we show that two members of this class, Nap1 and Vps75, bind histones in the tetrameric conformation also observed when they are sequestered within the nucleosome. Furthermore, H3 and H4 trapped in their tetrameric state can be used as substrates in nucleosome assembly and chaperone-mediated lysine acetylation. This alternate mode of histone interaction provides a potential means of maintaining the integrity of the histone tetramer during cycles of nucleosome reassembly

Numerical simulation of graded band gap GaAs/AlGaAs heterojunction solar cell by AMPS-1D

The conduction band discontinuity or spike in an abrupt heterojunction p+ GaAs / NAl0.4 Ga0.6As solar cell can hinder the separation of hole-electron by electric field. This paper analyzes the GaAs /AlxGa1-xAs/Al0.4Ga0.6As based solar cell performance by AMPS-1D numerical modeling. The affect of graded band gap region in the interface between the emitter (GaAs) and base (Al0.4Ga0.6As) on the solar cell’s performance is investigated. Among the factors studied are thickness of graded band gap region, thickness of emitter layer of the cells. In this study, a width 0.14µm has been required to eliminate the spike and improved the performance of solar cell. Keywords: heterojunction solar cell; graded band gap; AMPS-1D

The Effect of Graded Band Gap Structure Inserted in the Multijunction Solar Cell

We have theoretically calculated the photovoltaic conversion efficiency of a monolithic dual-graded junction AlGaAs/GaInAs device, which can be experimentally fabricated. By optimizing the band-gap combination of the considered structure, an improvement of conversion efficiency has been observed in comparison to the conventional AlGaAs/GaInAs system. For the suggested graded band-gap combination, our calculation indicates that the attainable efficiency can be enhanced up to 34% ( AM1.5d). Keywords: band gap gradient, multijunction solar cells, AlGaAs, GaInA

Determinants de la production dans les exploitations agricoles de la vallee du fleuve dans la commune de Kourtheye au Niger

L’intérêt d’identifier les déterminants de la production dans un contexte de pauvreté et de rareté des facteurs de production s’impose. C’est pourquoi la présente étude a pour objectif de contribuer à la connaissance de ces facteurs de production dans les exploitations agricoles de la commune rurale de Kourthèye. La méthodologie adoptée pour conduire l’étude a combiné la recherche documentaire et les enquêtes de terrain. Ces dernières ont concerné un échantillon de 125 exploitants choisis de manière aléatoire. Une classification et une caractérisation des agriculteurs ont été faites par l’Analyse en Composantes Principales (ACP) et la classification de Nuée dynamique. Elles ont été suivies d’une modélisation économétrique des données selon Cobb-Douglas dans sa forme logarithmique. L’étude révèle que l’ensemble des chefs des ménages enquêtés sont des hommes, présentant un âge moyen de 51 ans avec une taille moyenne des ménages de 10 personnes. Après analyse de variances, les facteurs travail, capital et santé ont été retenus et expliquent à eux seuls plus de 68 % des variations totales observées. La classification de Nuée Dynamique, regroupant les producteurs en trois classes homogènes A, B et C montre que les exploitations de type (A) et (B) se caractérisent principalement par des superficies cultivées limitées en cultures irriguées et forte mobilisation de la main d’œuvre familiale. Le facteur santé présente une corrélation négative (- 0 ,48) avec la production en culture irriguée de même (- 0,012) avec la culture sèche. L’application de la formule de Cobb Douglas, donne les facteurs explicatifs de la production et leurs coefficients. Mots clés : Déterminants, cultures irriguées, cultures sèches, facteur de production, exploitations agricoles, commune de Kourthèye.   English Title: Determinants of farming production in the River Valley of Kourtheye The interest of identifying the determinants of production in a poverty and scarcity context of production factors is essential. This is why this study aims to contribute to the knowledge of these factors of production on farms in the rural commune of Kourthèye. The methodology adopted to conduct the study combined Documentary Research with field surveys. These concerned a sample of 125 farmers. A classification and characterization of the farmers were made by the principal components analysis (PCA) and the  classification of Dynamic cloud. They are followed by an econometric modelling of the data according to Cobb-Douglas in its  logarithmic form. The study reveals that all the heads of the households surveyed are exclusively men, with an average age of 51 years with an average household size of 10 peoples. After analyzing the variance, the labour, capital and health factors were selected and alone explain more than 68% of the total variations observed. The classification of Dynamic Cloud, grouping producers into three homogeneous classes A, B and C shows that operators of type (A) and (B) are mainly characterized by cultivated areas limited to  irrigated crops and strong mobilization of family work force. The health factor is negatively correlated regardless of the type of  cropping. The health factor shows a negative correlation regardless of the type of crop. The application of the Cobb Douglas formula gives the explanatory factors of production and their coefficients. Keywords: determinants, irrigated crops, dry crops, production factor, farming, Kourthèye municipalit

Variabilité des précipitations au sahel Central et Recherche du forcage climatique par analyse du signal : la station de Maïne-Soroa (SE Niger) entre 1950 et 2005. Rainfall variability in the Central Sahel and climate forcing by signal analysis: Maïné-Soroa station (SE Niger) over the period 1950-2005

International audienceUne régression polynomiale non-paramétrique (méthode LOESS) appliquée aux précipitations annuelles de Maïné-Soroa (SE Niger) montre trois périodes : humide (1950-1967), aride (1968-1993), semi-aride (1994-2005). L'utilisation de la transformée en ondelettes continues permet de séparer la variabilité interne (haute fréquence) et la variabilité forcée (basse fréquence). Nous avons pu mettre en évidence sept modes de fréquence localisés dans le temps : deux modes intra-saisonniers (4-9jrs, 16-20jrs), deux modes saisonniers (6 mois, 1an), deux modes pluriannuels (2-4ans et 5-8ans) et un mode quasi-décennal (12-18ans). Lors du régime humide, on retrouve une forte variance des modes saisonniers liés à la ZCIT et des modes pluriannuels se succédant dans le temps (5-8ans puis 2-4ans) en liaison avec les températures de l'Atlantique Tropical Nord (TNA) puis avec l'Anticyclone des Açores. Ces modes basses fréquences sont synchrones avec une activité convective mature (mode 4-9jrs) et l'apparition d'une perturbation (mode 16-20jrs) lors de la transition entre la phase océanique et la phase continentale de la mousson. Au contraire, lors des années arides on retrouve le mode quasi-décennal, en lien avec les températures de l'Atlantique Tropical Sud (TSA), forçant une activité convective peu développée et perturbée au coeur de la phase continentale. A non-parametric polynomial regression applied to the Maine-Soroa annual rainfall timeseries reveals three periods: wet (1950-1967), arid (1968-1993) and semi-arid (1994-2005). Continuous Wavelet Transform allows crossing internal variability (high frequency) and forcing variability (low frequency). We could reveal seven frequency modes highly localized in time: two intraseasonal modes (4-9 days, 16-20 days), two seasonal modes (6mo, 1yr), two interannuals modes (2- 4yrs, 5-8yrs) and one quasidecadal mode (12-18yrs). During wet period, we notice a strong variance across seasonal modes in relation to ITCZ and the two interannual modes succeeding in time (5-8yrs then 2-4yrs) in connection with the Tropical North Atlantic temperatures (TNA) then Azores high. At the same time, we notice great convective activity (4-9days) and the oceanic/continental transition phase disturbation (16-20days). During the arid period, we notice the quasidecadal mode in relation with the Tropical South Atlantic temperatures (TSA), forcing a weak convective activity and disturbed in the medium of the continental phase

Effect of ciprofloxacin incorporation in PVA and PVA bioactive glass composite scaffolds

International audienceScaffolds are implants used to deliver cells, drugs, and genes into the body in a local controlled release pattern which offers many advantages over systematic drug delivery. Composite scaffolds of polyvinyl alcohol (PVA) and quaternary bioactive glass (46S6 system) with different ratios of glass contents were prepared by the lyophilisation technique. The broad spectrum antibiotic ciprofloxacin (Cip) was impregnated to the scaffold during the fabrication in a concentration of 5, 10 and 20%. Biodegradation rate and in-vitro mineralization of the prepared scaffolds were performed by soaking the scaffolds in simulated body fluid (SBF). Phase identification, microstructure, porosity, bioactivity, mechanical properties and drug release pattern in PBS were characterized by XRD, SEM coupled with EDS, Hg-porosimeter, inductively coupled plasma-optical emission spectroscopy (ICP-OES), universal testing machine, fourier transform infrared (FTIR) and UV-spectrophotometer, respectively. A porous scaffold has been obtained with porosity up to 85%. By increasing the glass contents in the prepared scaffold the porosity and the degradation rate decrease however, the compressive strength was enhanced. A sustained drug release pattern was observed with a quasi-Fickian diffusion mechanism. The formulated ciprofloxacin loaded porous polyvinyl alcohol scaffold gave an acceptable physicochemical properties and was able to deliver the drug in a prolonged release pattern which offers a distinguish treatment for osteomylitis as well as local antibacterial effect

Disulfide cross-links in the interaction of a cataract-linked αA-crystallin mutant with βB1-crystallin

AbstractA number of αA-crystallin mutants are associated with hereditary cataract including cysteine substitution at arginine 49. We report the formation of affinity-driven disulfide bonds in the interaction of αA-R49C with βB1-crystallin. To mimic cysteine thiolation in the lens, βB1-crystallin was modified by a bimane probe through a disulfide linkage. Our data suggest a mechanism whereby a transient disulfide bond occurs between αA- and βB1-crystallin followed by a disulfide exchange with cysteine 49 of a neighboring αA-crystallin subunit. This is the first investigation of disulfide bonds in the confine of the chaperone/substrate complex where reaction rates are favored by orders of magnitude. Covalent protein cross-links are a hallmark of age-related cataract and may be a factor in its inherited form