Temperature-Sensitive Mutations in the Putative Herpes Simplex Virus Type 1 Terminase Subunits pU L 15 and pU L 33 Preclude Viral DNA Cleavage/Packaging and Interaction with pU L 28 at the Nonpermissive Temperature

Terminases comprise essential components of molecular motors required to package viral DNA into capsids in a variety of DNA virus systems. Previous studies indicated that the herpes simplex virus type 1 UL 15 protein (pUL 15) interacts with the pUL 28 moiety of a pUL 28-pUL 33 complex to form the likely viral terminase. In the current study, a novel temperature-sensitive mutant virus was shown to contain a mutation in UL 33 codon 61 predicted to change threonine to proline. At the nonpermissive temperature, this virus, designated ts8-22, replicated viral DNA and produced capsids that became enveloped at the inner nuclear membrane but failed to form plaques or to cleave or package viral DNA. Incubation at the nonpermissive temperature also precluded coimmunoprecipitation of UL 33 protein with its normal interaction partners encoded by UL 28 and UL 15 in ts8-22-infected cells and with pUL 28 in transient-expression assays. Moreover, a temperature-sensitive mutation in UL 15 precluded coimmunoprecipitation of pUL 15 with the UL 28 and UL 33 proteins at the nonpermissive temperature. We conclude that interactions between putative terminase components are tightly linked to successful viral DNA cleavage and packaging.