HERPESVIRUS OF TURKEYS HOMOLOG OF HSV VP16 IS STRUCTURALLY RELATED TOVARICELLA-ZOSTER VIRUS TRANS-INDUCING PROTEIN ENCODED BY ORF-10

Expression of the immediate-early genes of a-herpesviruses is stimulat ed by a family of trans-inducing factors represented by VP16 of HSV-1 and ORF10 gene product of VZV. We have identified and determined the n ucleotide sequence of the UL48 gene encoding the herpesvirus of turkey s (HVT) homologue of HSV VP16, The gene maps to the BamHI-J fragment a nd appears to be expressed in a form of bicistronic transcript togethe r with UL49. The deduced amino acid sequence of the protein encoded by HVT UL48 gene shows 55% identity with MDV UL48 gene product, Like the majority of related proteins in other alpha-herpesviruses, the protei n encoded by HVT UL48 gene lacks the acidic C-terminal tail, known to possess the transactivation capacity of HSV VP16. Hydrophobic cluster analysis has revealed that its predicted domain composition is closely related to the transactivator protein encoded by ORF10 of VZV, Howeve r, the putative amino-terminal activation domain of the HVT homologue of HSV VP16 does not contain a typical horseshoe-like hydrophobic clus ter found in other alpha-herpesvirus homologues, suggesting either tha t it acts as a transactivator via a different activation domain or tha t its transactivation potential is diminished.