Probing FinO-FinP RNA interactions by site-directed protein-RNA crosslinking and gelFRET

The conjugative transfer of F-plasmids is repressed by a two-component system, which consists of the antisense RNA FinP and the protein FinO. FinO binds FinP, protecting it from endonucleolytic degradation and facilitating duplex formation between FinP and its complementary RNA. Here we present the results of site-specific protein-RNA cross-linking and gel-based fluorescence resonance energy transfer (gelFRET) experiments used to probe the structure of a complex of FinO bound to an RNA target consisting of a duplex with 5' and 3' single-stranded tails. The crosslinking experiments reveal that an extensive, largely positively charged surface on FinO contacts RNA. The gelFRET measurements indicate that the 5' single-stranded tail of the RNA is in closer contact with much of the protein than the distal, blunt end of the RNA duplex. These data suggest that significant conformational adjustments in the protein and/or the RNA accompany complex formation.     

Quatre champignons nouveaux de la R. S. Roumaine

Sans résumé     

Stratification in the central nervous system]

Stratigenesis in the optic tectum of developing chick embryos was investigated between the 4th and the 11th day of incubation. Stratification is achieved by successive emigration of cell contigents from the proliferative layer. In the opinion of the authors the main factor which determines this very regular cell migration would be a gradient of oxygen and of metabolites. The gradient has to appear in the wall of tectum due to its typical vascular network. Experiences with induced hypoxia or with selective damage of the proliferative layer strengthen the hypotesis of an oxygen gradient playing the role of a generally active epigenetic factor in the stratigenesis of the central nervous system.     

Understanding the impact of correlation within pair‐bonds on Cormack–Jolly–Seber models

1. The Cormack–Jolly–Seber (CJS) model and its extensions have been widely applied to the study of animal survival rates in open populations. The model assumes that individuals within the population of interest have independent fates. It is, however, highly unlikely that a pair of animals which have formed a long‐term pairing have dissociated fates.
2. We examine a model extension which allows animals who have formed a pair‐bond to have correlated survival and recapture fates. Using the proposed extension to generate data, we conduct a simulation study exploring the impact that correlated fate data has on inference from the CJS model. We compute Monte Carlo estimates for the bias, range, and standard errors of the parameters of the CJS model for data with varying degrees of survival correlation between mates. Furthermore, we study the likelihood ratio test of sex effects within the CJS model by simulating densities of the deviance. Finally, we estimate the variance inflation factor c^ for CJS models that incorporate sex‐specific heterogeneity.
3. Our study shows that correlated fates between mated animals may result in underestimated standard errors for parsimonious models, significantly deflated likelihood ratio test statistics, and underestimated values of c^ for models taking sex‐specific effects into account.
4. Underestimated standard errors can result in lowered coverage of confidence intervals. Moreover, deflated test statistics will provide overly conservative test results. Finally, underestimated variance inflation factors can lead researchers to make incorrect conclusions about the level of extra‐binomial variation present in their data.

     

Cross-linked amylose as matrix for drug controlled release. X-ray and FT-IR structural analysis

For cross-linked amylose (CLA) tablets prepared by direct compression, a linear increase in cross-linking degree (cld) defined as percentage of epichlorohydrin cross-linker/polymer, generates non-monotonous variation of drug release time. Controlled release (up to 20–24 h) properties were obtained only for tablets from CLA (Contramid^TM) with relatively low cld (CLA-2 up to CLA-6). Moderate increase in cld (CLA-15) generates a sharp decrease in the release time (2–6 h). This is a particular characteristic of the CLA matrix. The controlled release properties were related to the X-ray pattern of the dry CLA network. The increase in cld induces a transition from B-type (double helix) to a predominat V-type (single helix) and to more amorphous conformation of CLA powders. Furthermore, FT-IR data indicated low free water content at low cld. For low cross-linked CLA, chains are closely located and stabilized by HO groups involved in hydrogen bonding and thus more resistant to hydration and more appropriate for the control of drug release.