ABSTRACT
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 UL15 protein (pUL15) interacts with the pUL28 moiety of a pUL28-pUL33 complex to form the likely viral terminase. In the current study, a novel temperature-sensitive mutant virus was shown to contain a mutation in UL33 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 UL33 protein with its normal interaction partners encoded by UL28 and UL15 in ts8-22-infected cells and with pUL28 in transient-expression assays. Moreover, a temperature-sensitive mutation in UL15 precluded coimmunoprecipitation of pUL15 with the UL28 and UL33 proteins at the nonpermissive temperature. We conclude that interactions between putative terminase components are tightly linked to successful viral DNA cleavage and packaging.
A temperature-sensitive mutation in a herpes simplex virus type 1 gene required for viral DNA synthesis maps to coordinates 0.609 through 0.614 in UL.