Virus transcript mapping studies in cells infected with temperature-sensitive mutants of herpes simples virus type 1.

Nuclear and cytoplastic transcripts, synthesized in cells infected with six DNA-negative temperature-sensitive (ts) mutants of HSV-1 (ts B, ts D, ts E, ts K, ts S and ts T) under non-permissive conditions, were isolated and hybridized to unlabelled fragments of HSV-1 DNA, generated by restriction endonuclease digestion and immobilized on to nitrocellulose membranes by the method of Southern (1975). In this way it has been possible to map those regions of the HSV-1 genome represented by stable transcrips in cells infected with these mutants and compare them with those regions transcribed in cells infected with the wild-type virus at early and late times post infection (before and after viral DNA replication) and in the presence of DNA- and protein-synthesis inhibitors. Viral transcription in ts D, ts T and ts K-infected cells is restricted, the patterns of hybridization being similar, but not identical to that observed with immediate early RNA. Since these three mutants fall into two complementation groups, these experiments suggest that at least two viral products are required for the switch-on of early transcripts. In contrast, transcript mapping with the other early mutants (ts B, ts E and ts S) has shown a much less restricted transcriptional pattern, the pattern obtained resembling that with early, rather than late RNA.