GENERIC ANALYSIS OF THE UL15 GENE LOCUS FOR THE PUTATIVE TERMINASE OFHERPES-SIMPLEX VIRUS TYPE-1

The herpes simplex virus (HSV-1) UL15 gene encodes one of the six vira l gene products required for viral DNA cleavage and packaging. UL15 is a spliced gene and encodes two separately translated proteins, UL15 a nd UL15.5. Sequence analysis reveals that UL15 shares homology with gp 17, the large catalytic subunit of the bacteriophage T4 terminase, a p rotein which cleaves the polymeric T4 DNA into monomers. Both proteins contain a putative ATP binding motif known as the Walker A and B boxe s. In this report, immunofluorescence was used to show that UL15 local izes to the nucleus in the absence of any other viral proteins; this i ndicates that UL15 contains its own nuclear localization signal. In ad dition, we found that UL15 colocalizes with replication compartments a t early times (6 h postinfection]. Since, at this time, preformed caps ids as well as other cleavage and packaging proteins are also recruite d to replication compartments it seems likely that cleavage and packag ing occurs in the same compartments in which DNA synthesis occurs. Als o in this report, we have investigated UL15.5, the N-terminally trunca ted gene product of the UL15 open reading frame [ORF). The start codon has been mapped to Met(443) within the UL15 ORF. Furthermore, we have shown that plasmids containing a UL15.5 knockout mutation still compl ement the growth of UL15 insertion mutant viruses, indicating that UL1 5.5 is not required for viral growth in cell culture. Last, we constru cted a UL15 mutant, UL15C(G263A), in which the invariant Gly(263) in t he Walker box A of the ATP binding motif (GKT) was substituted with an alanine. We show that the mutant gene fails to support the growth of UL15 insertion mutant viruses, indicating that the putative ATP bindin g motif of UL15 is indispensable for its function. (C) 1998 Academic P ress.