Secretion of Genome-Free Hepatitis B Virus – Single Strand Blocking Model for Virion Morphogenesis of Para-retrovirus

As a para-retrovirus, hepatitis B virus (HBV) is an enveloped virus with a double-stranded (DS) DNA genome that is replicated by reverse transcription of an RNA intermediate, the pregenomic RNA or pgRNA. HBV assembly begins with the formation of an “immature” nucleocapsid (NC) incorporating pgRNA, which is converted via reverse transcription within the maturing NC to the DS DNA genome. Only the mature, DS DNA-containing NCs are enveloped and secreted as virions whereas immature NCs containing RNA or single-stranded (SS) DNA are not enveloped. The current model for selective virion morphogenesis postulates that accumulation of DS DNA within the NC induces a “maturation signal” that, in turn, triggers its envelopment and secretion. However, we have found, by careful quantification of viral DNA and NCs in HBV virions secreted in vitro and in vivo, that the vast majority of HBV virions (over 90%) contained no DNA at all, indicating that NCs with no genome were enveloped and secreted as empty virions (i.e., enveloped NCs with no DNA). Furthermore, viral mutants bearing mutations precluding any DNA synthesis secreted exclusively empty virions. Thus, viral DNA synthesis is not required for HBV virion morphogenesis. On the other hand, NCs containing RNA or SS DNA were excluded from virion formation. The secretion of DS DNA-containing as well as empty virions on one hand, and the lack of secretion of virions containing single-stranded (SS) DNA or RNA on the other, prompted us to propose an alternative, “Single Strand Blocking” model to explain selective HBV morphogenesis whereby SS nucleic acid within the NC negatively regulates NC envelopment, which is relieved upon second strand DNA synthesis

Exploring new physics frontiers through numerical relativity

The demand to obtain answers to highly complex problems within strong-field gravity has been met with significant progress in the numerical solution of Einstein's equations - along with some spectacular results - in various setups. We review techniques for solving Einstein's equations in generic spacetimes, focusing on fully nonlinear evolutions but also on how to benchmark those results with perturbative approaches. The results address problems in high-energy physics, holography, mathematical physics, fundamental physics, astrophysics and cosmology

Analysis of oxidative events induced by expanded polyglutamine huntingtin exon 1 that are differentially restored by expression of heat shock proteins or treatment with an antioxidant

We recently reported that the transient expression of polyglutamine tracts of various size in exon 1 of the huntingtin polypeptide (httExl) generated abnormally high levels of intracellular reactive oxygen species that directly contributed to cell death. Here, we compared the protection generated by heat shock proteins to that provided by the antioxidant agent N-acetyl-L-cysteine. In cells expressing httExl with 72 glutamine repeats (httEx1-72Q), the overexpression of Hsp27 or Hsp70 plus Hdj-1(Hsp40) or treatment of the cells with N-acetyl-L-cysteine inhibited not only mitochondrial membrane potential disruption but also the increase in reactive oxygen species, nitric oxide and protein oxidation. However, only heat shock proteins and not N-acetyl-L-cysteine reduced the size of the inclusion bodies formed by httExl-72Q. In cells expressing httExl polypeptide with 103 glutamine repeats (httEx1-103Q), heat shock proteins neither decreased oxidative damage nor reduced the size of the inclusions. In contrast, N-acetyl-L-cysteine still efficiently decreased the oxidative damage induced by httExl-103Q polypeptide without altering the inclusions. N-Acetyl-L-cysteine was inactive with regard to proteasome inhibition, whereas heat shock proteins partially restored the caspase-like activity of this protease. These observations suggest some relationships between the presence of inclusion bodies and the oxidative damage induced by httExl-polyQ