IDENTIFICATION AND ANALYSIS OF THE SIMIAN VARICELLA VIRUS THYMIDINE KINASE GENE

The thymidine kinase (TK) of herpesviruses, in contrast to cellular TK s, phosphorylates a variety of substrates including antiherpetic nucle oside analogues. This study reports the identification and DNA sequenc e of the simian varicella virus (SVV) TK gene. A P-32-labeled varicell a tester virus (VZV) TK DNA probe hybridized to the HindIII B subclone of the SVV BamHI B restriction endonuclease (RE) fragment, indicating the presence of a SVV DNA sequence homologous to the VZV TK gene. DNA sequence analysis of the SVV HindIII B subclone revealed a 1014 base pair (bp) open reading frame (ORF) encoding a 337 amino acid polypepti de homologous to herpesvirus TKs. The predicted SVV and VZV TK polypep tides share 51.3% identity, and alignment of the putative protein sequ ence of several TK homologues suggests the position of a conserved nuc leotide binding site and a nucleoside (substrate) binding site in the SVV TK. Identification of the 5' end of the SVV TK transcript by prime r extension analysis allowed a comparison of the SVV and VZV TK promot er regions indicating extensive conservation of the DNA sequence and t ranscription factor binding sites. Plaque reduction assays demonstrate that the SVV TK is active based on the susceptibility of SVV to acycl ovir treatment and that SVV is less sensitive to acyclovir than VZV an d herpes simplex virus (HSV-1) in infected Vero cells. Identification of the SVV TK ORF will facilitate studies that examine the role of vir al TKs in pathogenesis and antiviral sensitivity and provides a potent ial insertion site for the expression of foreign genes.