Herpes simplex virus (HSV) and Varicella-Zoster virus (VZV) are alphaherpes viruses that cause oral/genital herpes and chickenpox/zoster respectively. They are enveloped viruses with relatively large genomes with the coding capacity for more than 70 unique genes. The expression of genes in alphaherpes viruses are temporally regulated and three putative kinetic classes have been defined: immediate early, early and late genes. The immediate early genes encode proteins that regulate the expression of genes of other kinetic classes thus playing a pivotal role in the life cycle of the herpesviruses. These alphaherpesviral immediate early proteins not only provide excellent model systems to study eukaryotic gene regulation in general but also understanding the regulatory mechanics of these proteins provide potential molecular targets that could be exploited for therapeutic interventions. Current efforts focus on four HSV regulatory proteins: ICP0, ICP4, ICP27 and VP16. We recently reported that the ICP27 is a RNA-binding protein and stabilizes unstable mRNA by specifically interacting with the 3' RNA-processing signals of a particular transcript. Extending these initial studies, we have mapped the domain of ICP27 that interacts with mRNA and also have identified a stem-loop structure in the RNA molecule that confers binding to ICP27. Furthermore, the ability of ICP27 to oligomerize in vivo has been demonstrated. In addition, the ability of this protein to interact with the basal transcription factors TFIIB and TBP has been established. These findings point to a novel and unique role for ICP27 in regulating HSV gene expression both transcriptionally and post-transcriptionally. In addition, to identify the cellular proteins that interact with HSV regulatory proteins to mediate their transcriptional effects, we have made use of the """"""""Yeast two hybrid"""""""" system. By screening cellular cDNA libraries derived from neuronal tissues and HeLa cells we have identified several cellular proteins that physically interact with this key regulatory protein of HSV. Ongoing studies are directed at delineating these protein-protein interactions as they relate to the function of ICP27 at the molecular level. The three VZV transregulatory proteins under investigation are IE62, ORF4 and ORF10. Our recent studies indicate that the IE62 - dependent activation of responsive promoters are mediated by a unique mechanism involving the TATA element of the promoter. Studies are in progress to delineate the interactions of IE62 with the transcriptional machinery of the Pol II promoters. In addition to the regulatory proteins of HSV, we have expanded our repertoire of proteins under study to include the ORF P and ICP34.5 proteins which appear to play significant roles in HSV biology. Again, using the """"""""Yeast two hybrid"""""""" system several cellular proteins that interact with these two HSV proteins have been identified and are being further characterized.
