BOVINE HERPESVIRUS-1 UL49.5 HOMOLOG GENE ENCODES A NOVEL VIRAL ENVELOPE PROTEIN THAT FORMS A DISULFIDE-LINKED COMPLEX WITH A 2ND VIRION STRUCTURAL PROTEIN

We previously reported that the genome of bovine herpesvirus 1 (BHV-1) contains an open reading frame (ORF) homologous to the herpes simplex virus UL49.5 ORF, and as with the herpes simplex virus UL49.5 ORF, th e deduced amino acid sequence of the BHV-1 UL49.5 homolog (UL49.5h) co ntains features characteristic of an integral membrane protein, implyi ng that it may constitute a functional gene encoding a novel viral env elope protein. This communication reports on the identification of the BHV-1 UL49.5h gene product. By employing an antibody against a synthe tic BHV-1 UL49.5h peptide and an UL49.5h gene deletion mutant, the pri mary product of BHV-1 UL49.5h gene was identified as a polypeptide wit h a size of approximately 9 kDa; in both infected cells and isolated v irions, the UL49.5h products were found to exist in three forms: monom er, disulfide-linked homodimer, and disulfide-linked heterodimer conta ining a second viral protein with a size of about 39 kDa. O-Glycosidas e digestion and [H-3]glucosamine labelling experiments showed that the UL49.5h protein is not glycosylated. Although the deduced amino acid sequence contains putative sites for myristylation and phosphorylation , we were unable to detect either modification. Surface labelling and trypsin digestion protection experiments showed that the BHV-1 UL49.5h protein was present on the surface of infected cells and on the surfa ce of mature virions. Nonionic detergent partition of isolated virions revealed that the UL49.5h protein is more tightly associated with the virion tegument-nucleocapsid structure than envelope protein go. The results from this study demonstrate that the BHV-1 UL49.5h gene encode s a nonglycosylated virion envelope protein which may associate with v irion internal structures by forming a complex,with the 39-kDa virion structural protein.