| Research Abstract |
The aim of the research was to investigate the mechanism of herpes simplex virus (HSV) latency. The results obtained during these two years were mainly as follows.
(i) ICP0 is an important regulatory protein that is involved in regulation both of gene expression in productive infection and latency. None of the known functions at the molecular level account for the apparent activity of ICP0 as a transactivator. Here we report that ICP0 functionally interacts with a cellular transcription factor BMAL1, a member of the bHLH-PAS super family of transcriptional regulators. Specifically, sequences mapped to the exon II of ICP0 interacted with BMAL1 in the yeast two-hybrid system and in reciprocal pull down experiments in vitro.Moreover, the enhancement of transcription of a luciferase reporter construct whose promoter contained multiple BMAL1 binding sites by ICP0 and BMAL1 was significantly greater than that observed by ICP0 or BMAL1 alone.These results indicate that ICP0 interacts physicall
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y and functionally with at least one cellular transcription-regulatory factor. (ii) An earlier report (Y.Kawaguchi, R.Bruni, and B.Roizman, J.Virol. 71 : 1019-1024,1997 ; Y.Kawaguchi, C.Van Sant, and B.Roizman, J.Virol. 72 : 1731-1736,1998) showed that herpes simplex virus 1 (HSV-1) infection causes the hyperphosphorylation of translation elongation factor 1δ (EF-1δ) and that the modification of EF-1δ is the consequence of direct phosphorylation by a viral protein Kinase encoded by the U_L13 gene of HSV-1. The U_L13 gene is conserved in members of all herpesvirus subfamilies. Here we report the following. (i) In various mammalian cells, accumulation of the hyperphosphorylated form of EF-1δ is observed after infection with alpha-, beta- and gammaherpesviruses including HSV-2, feline herpesvirus type 1, pseudorabisvirus, and bovine herpesvirus type 1, human cytomegalovirus (HCMV) and equine herpesvirus type 2. (ii) In HLF cells infected with recombinant HSV-1 lacking U_L13 gene, the hypophosphorylated form of EF-1δ is a minor species, whereas the relative amount of the hyperphosphorylated form of EF-1δ significantly increases in cells infected with the recombinant HSV-1 in which U_L13 is replaced by HCMV U_L97, a homologue of U_L13. These results indicate that the post-translational modification of EF-1δ is conserved herpesvirus function and the U_L13 homologues may be responsible for the universal-modification of the translation factor. Less
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