Functional Characterization of the Putative Hepatitis B Virus Core Protein Late Domain Using Retrovirus Chimeras

The hepatitis B virus (HBV) Core protein encodes a late (L)-domain like motif (₁₂₉PPAYRPPNAP¹³⁸) that has been purported to serve as a docking site for recruitment of host factors such as Nedd4 that can mediate viral particle release from infected cells. However, mutation of this region of Core typically disrupts nucleocapsid formation in the cytoplasm, making it difficult to ascertain if the Core PPAY motif constitutes a functional L-domain that mediates HBV release in the context of replicating virus. Since many viral L-domains are functionally interchangeable between different virus families, and such swapping experiments have been used as a tool to identify other viral sequences with L-domain activity, we generated chimeric constructs between murine leukemia virus (MLV) Gag and HBV Core to determine if the potential HBV L-domain motif is sufficient to stimulate virus release. We found that the HBV Core PPAY motif, but not the PNAP motif, demonstrates L-domain activity in the context of MLV replication to direct virus release and infectious virion production. Additionally, we found that overexpression of the cellular Nedd4 or WWP1 ubiquitin ligases stimulates release of a partially defective PPAY domain mutant, providing further evidence supporting a role for the Nedd4 ubiquitin ligase in promoting HBV release. These studies lend further insight into the mechanisms used by HBV to mediate its release from infected cells.     

Combined effects of CO2 and light on large and small isolates of the unicellular N2-fixing cyanobacterium Crocosphaera watsonii from the western tropical Atlantic Ocean

We examined the combined effects of light and pCO₂ on growth, CO₂-fixation and N₂-fixation rates by strains of the unicellular marine N₂-fixing cyanobacterium Crocosphaera watsonii with small (WH0401) and large (WH0402) cells that were isolated from the western tropical Atlantic Ocean. In low-pCO₂-acclimated cultures (190 ppm) of WH0401, growth, CO₂-fixation and N₂-fixation rates were significantly lower than those in cultures acclimated to higher (present-day ～385 ppm, or future ～750 ppm) pCO₂ treatments. Growth rates were not significantly different, however, in low-pCO₂-acclimated cultures of WH0402 in comparison with higher pCO₂ treatments. Unlike previous reports for C. watsonii (strain WH8501), N₂-fixation rates did not increase further in cultures of WH0401 or WH0402 when acclimated to 750 ppm relative to those maintained at present-day pCO₂. Both light and pCO₂ had a significant negative effect on gross : net N₂-fixation rates in WH0402 and trends were similar in WH0401, implying that retention of fixed N was enhanced under elevated light and pCO₂. These data, along with previously reported results, suggest that C. watsonii may have wide-ranging, strain-specific responses to changing light and pCO₂, emphasizing the need for examining the effects of global change on a range of isolates within this biogeochemically important genus. In general, however, our data suggest that cellular N retention and CO₂-fixation rates of C. watsonii may be positively affected by elevated light and pCO₂ within the next 100 years, potentially increasing trophic transfer efficiency of C and N and thereby facilitating uptake of atmospheric carbon by the marine biota.     

Intrinsically disordered Meningioma-1 stabilizes the BAF complex to cause AML

1. Download : Download high-res image (137KB)
2. Download : Download full-size image

     

Multivariate frailty models for two types of recurrent events with a dependent terminal event: Application to breast cancer data

Individuals may experience more than one type of recurrent event and a terminal event during the life course of a disease. Follow‐up may be interrupted for several reasons, including the end of a study, or patients lost to follow‐up, which are noninformative censoring events. Death could also stop the follow‐up, hence, it is considered as a dependent terminal event. We propose a multivariate frailty model that jointly analyzes two types of recurrent events with a dependent terminal event. Two estimation methods are proposed: a semiparametrical approach using penalized likelihood estimation where baseline hazard functions are approximated by M‐splines, and another one with piecewise constant baseline hazard functions. Finally, we derived martingale residuals to check the goodness‐of‐fit. We illustrate our proposals with a real dataset on breast cancer. The main objective was to model the dependency between the two types of recurrent events (locoregional and metastatic) and the terminal event (death) after a breast cancer.     

EVIDENCE FOR A MOSAIC HYBRID ZONE IN THE GRASS SHRIMP PALAEMONETES KADIAKENSIS (PALAEMONIDAE) AS REVEALED BY MULTIPLE GENETIC MARKERS

Molecular techniques provide powerful tools for studying the geographic structure of hybrid zones and the dynamics of gene exchange between incipient species. We examined allozyme variation at five loci (PGM, GPI, MDH-1, MDH-2, and LDH) for 27 populations of Palaemonetes kadiakensis from the central, coastal, and eastern regions of Texas. Central Texas populations of P. kadiakensis exhibited highly significant linkage disequilibrium and departures from Hardy-Weinberg genotype proportions. In populations with linkage disequilibrium, allelic differences at GPI defined two types of P. kadiakensis, designated A and B. Both types existed in central Texas with little or no evidence of interbreeding, whereas the populations from all other localities showed complete introgression of type B alleles into the type A gene pool. We also examined ribosomal DNA (rDNA) and mitochondrial DNA (mtDNA) variation in a subset of populations, chosen to cover a range of geographic locations and levels of linkage disequilibrium. Two groups of mtDNA haplotypes and two restriction fragment patterns for the rDNA corresponded to allozyme type A and B individuals in populations exhibiting linkage disequilibrium. In populations with ongoing hybridization, all hybrid animals (N= 15) exhibited type A mtDNA. Exhibition of type A mtDNA indicated that type A females had mated successfully with type B males, but type B females had not mated successfully with type A males. Genotype distributions suggest reduced reproduction by hybrid offspring in central Texas populations. These patterns are consistent with a mosaic model of hybrid zone dynamics.     

Thermodynamics of nucleotides binding to phosphorylase b.

The effects of several chemical modifications in the AMP molecule on its interaction with phosphorylase b are examined by microcalorimetry, equilibrium dialysis, light scattering and ultracentrifuge experiments. In this work we report the results obtained for eight AMP analogues corresponding to different substituents in the puric base or in the ribose, or to different positions of the phosphate. The thermodynamic properties of the interaction between the phosphorylase b and the above mentioned nucleotides are also reported. The following conclusions were obtained: a) Except for IMP and 2'dIMP all the nucleotides studied clearly show two types of binding sites in the enzyme. b) The interaction of the nucleotide with its weaker affinity binding site is highly dependent upon chemical alterations in the puric base. c) Both the amino group in C(6) and the N(1) of the adenine in the AMP seem to play an important role in the conformational transitions induced by the nucleotide on the enzyme. d) The tetramerization of phosphorylase b in the presence of 10(-2) M AMP and in the conditions of the ultracentrifuge experiments is drastically affected by modifications in the ribose-phosphate part of the AMP molecule.     

Genotype-specific interactions and the trade-off between host and parasite fitness

Background  

Evolution of parasite traits is inextricably linked to their hosts. For instance one common definition of parasite virulence is the reduction in host fitness due to infection. Thus, traits of infection must be viewed in both protagonists and may be under shared genetic and physiological control. We investigated these questions on the oomycete Hyaloperonospora arabidopsis (= parasitica), a natural pathogen of the Brassicaceae Arabidopsis thaliana.     

Isolation and characterization of a new virus from owl monkeys: herpesvirus aotus type 3

Owl monkey kidney cell cultures yielded a viral agent 32 days after initiation of the culture. The virus was identified as a herpesvirus by physico-chemical, cultural, and morphological features. Serologically this herpesvirus was found to be unrelated to other members of this family, as well as to Herpesvirus aotus type 1 and 2. Based on these findings the name Herpesvirus aotus type 3 is suggested for this herpesvirus.