Herpesvirus Of Turkeys Homologue Of Hsv Vp16 Is Structurally Related To Varicella Zoster Virus Trans-Inducing Protein Encoded By Orf 10

Expression of the immediate-early genes of alpha-herpesviruses is stimulated 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 nucleotide sequence of the
UL48 gene encoding the herpesvirus of turkeys (HVT) homologue of HSV VP16. The
gene maps to the BamHI-J fragment and appears to be expressed in a form of
bicistronic transcript together 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 protein
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. However, the putative amino-terminal activation
domain of the HVT homologue of HSV VP16 does not contain a typical horseshoe-like
hydrophobic cluster found in other alpha-herpesvirus homologues, suggesting
either that it acts as a transactivator via a different activation domain or that
its transactivation potential is diminished.