The activation of a viral late gene by herpes simplex virus type 1 ICP27

The herpes simplex virus type 1 (HSV-1) immediate-early protein ICP27 has been shown to activate the expression of a subset of viral delayed early and late genes. The goal of the research described in this thesis was to characterize the molecular mechanism or mechanisms by which ICP27 activates responsive viral genes. To investigate the mechanism of gene induction by ICP27, we have focused on the true L gene encoding the glycoprotein C (gC) as a model viral target gene. We chose to use the gC gene because it is highly dependent upon ICP27 during viral infection, at both the protein and mRNA levels.; We demonstrate that the gC gene is specifically transactivated by ICP27 in transfected Vero cells and that this transactivation is independent of other viral proteins. Using various gC plasmid constructs, we show that ICP27's stimulatory effects are independent of the gC gene's endogenous promoter and polyadenylation site.; Using nuclear run-on transcription assays to examine the activation of the stably-transfected gC gene, we show that transcriptional induction of the gC genes is ICP27-independent. In contrast, accumulation of gC mRNA is very highly dependent on ICP27. Together, these results indicate that ICP27 activation occurs post-transcriptionally. Moreover, our results suggest that the gC message is being rapidly degraded when ICP27 is absent and that ICP27 functions to stabilize gC mRNA.; We also used the gC gene derivatives in transfection assays to attempt to map an ICP27 responsive element (27-RE) in the gC gene. Our results indicate that the gC gene contains multiple 27-REs that contribute to ICP27 activation. We were able to map one 27-RE to the gC gene's 5' untranslated region. We were also able to identify a region of the 5' UTR that is critical for the accumulation of gC protein. Using a panel of ICP27 mutants and homologs to discern what ICP27 domains are required for gC activation, we demonstrate that the C-terminal residues of the ICP27 polypeptide are critical for the ability to activate gC expression.