A dominant lethal temperature-sensitive mutant of herpes simplex virus type 1

Abstract

A temperature-sensitive ( ts) mutant of herpes simplex virus type 1 (HSV-1), ts P23, markedly inhibited the growth of the wild-type virus from which it was derived in mixed infectiobs at the nonpermissive temperature. When cells were mixedly infected with equal multiplicities of ts P23 and other HSV-1 mutants, complementation was inefficient. However, complementation indices increased as the multiplicity of ts P23 decreased relative to that of the other mutant, indicating that interference by tsP23 is a function of the dose of the mutant gene. Biochemically, ts P23 is DNA-negative, overproduces certain immediate early and delayed early viral polypeptides, and underproduces late, structural gene products. Patterns of viral DNA and protein synthesis in cells mixedly infected with ts P23 and the wild-type virus at the nonpermissive temperature were similar to those of cells infected with the mutant alone at this temperature. Temperature-shift studies and the kinetics of interference by ts P23 with the growth of the wild-type virus indicate that the mutant is arrested early in the replicative cycle. In support of this hypothesis is the observation that viral polypeptide synthesis in cells infected with ts P23 at 39° was similar but not identical to that observed in cells infected with the wild-type virus in the presence of phosphonoacetic acid, a drug which is thought to act directly on the viral DNA polymerase molecule, a delayed-early viral gene product. The interfering properties of the mutant, the timing of the inhibitory effect, and the kinetics of protein synthesis in mutant-infected cells at 39° indicate that ts P23 is a dominant lethal mutant with a primary defect in a “trans” acting, delayed early gene function essential for viral DNA synthesis.