ISOLATION AND CHARACTERIZATION OF HERPES-SIMPLEX VIRUS TYPE-1 MUTANTSDEFECTIVE IN THE UL6 GENE

Previous studies have shown that the protein encoded by herpes simplex virus type 1 (HSV-1) gene UL6 is required for processing and packagin g of replicated viral DNA and is a minor component of virions and caps ids. In this report, we describe the construction of UL6(-) HSV-1 muta nts with a disrupted UL6 gene using complementing cells and show that they fail to synthesize the UL6 protein or produce infectious virus in noncomplementing cells. The mutants synthesized but failed to process and encapsidate viral DNA and accumulated only immature capsids which lacked the UL6 protein. Immunofluorescence analysis showed that the U L6 protein, when expressed transiently in transfected cells in the abs ence of other HSV-1 proteins, is localized exclusively to the nucleus. We also investigated an HSV-1 mutant with a defect in gene UL33, the product of which is also thought to be involved in viral DNA processin g and packaging. The phenotype of this mutant on noncomplementing cell s with regard to failure to process and encapsidate viral DNA, accumul ation of immature capsids, and inability to produce infectious virus w as the same as that of UL6(-) viruses. This mutant, however, produced capsids containing the UL6 protein, indicating that association of the UL6 protein with the capsid is independent of the UL33 protein. (C) 1 996 Academic Press, Inc.