Synthesis of virus DNA and polypeptides by temperature-sensitive mutants of rabbitpox virus

Eighteen temperature-sensitive (ts) mutants of rabbitpox virus were examined for defects in synthesis of DNA and protein. Two mutants (ts-3 and ts-16) were defective in DNA synthesis (DNA-), since both incorporated significantly less than wild-type amounts of labelled thymidine into acid-precipitable material when infected cells were incubated at the restrictive temperature. Both these mutants gave only the 'early' class of virus polypeptides when infected cell extracts were examined by SDS--polyacrylamide slab gel electrophoresis following incubation at 40 degrees C. Nine of the remaining sixteen DNA+ ts mutants (ts-1, ts-2, ts-6, ts-12, ts-15, ts-17, ts-31, ts-32 and ts-33) synthesized wild-type levels of most virus polypeptides at 40 degrees C; six DNA+ ts mutants (ts-7, ts-8, ts-9, ts-11, ts-23 and ts-24) were defective in the post-translational cleavage of the polypeptides involved in membrane stabilization and particle assembly; one DNA+ ts mutant (ts-14) synthesized only the 'early' class of virus polypeptides, implying that either replicated DNA was not fully functional or that a specific early function was required for late transcription.