Temperature-sensitive mutants of herpes simplex virus type 1 defective in transcriptional and post-transcriptional functions required for viral DNA synthesis

DNA- temperature-sensitive (ts) mutants of herpes simplex virus (HSV) in four complementation groups (A, B, C, and D) were examined in temperature shift-down experiments to determine whether viral DNA synthesis was inhibited at the level of transcription or translation at the nonpermissive temperature. The mutant in group D synthesized viral DNA following shift-down in the presence of actinomycin D, whereas mutants in groups A, B, and C did not. These results demonstrate that mutants in the latter three groups are defective in transcriptional functions, whereas the group D mutant is defective in a post-transcriptional function required for viral DNA synthesis. The time required for recovery of DNA synthetic capabilities following shift-down for mutants in groups B and C was found to be approximately 2 hr. Transcripts specifying the D gene product were shown to be synthesized at the nonpermissive temperature by 2 hr postinfection. Polypeptide synthesis by all four mutants following shift-down in the presence of inhibitor was similar to that observed in mutant-infected cells maintained continuously at the nonpermissive temperature in the absence of inhibitor. Restoration of the wild-type pattern of viral polypeptide synthesis following shift-down in the presence of inhibitor was greater for the A, C, and D mutants than for mutants in group B.