MUTATIONAL ANALYSIS OF THE HERPES-SIMPLEX VIRUS TYPE-1 STRICT LATE UL38 PROMOTER LEADER REVEALS 2 REGIONS CRITICAL IN TRANSCRIPTIONAL REGULATION

The unusual TATA homology TTTAAA at -31 relative to the transcriptional start site of the herpes simplex virus type 1 (HSV-1) strict late (gamma) U(L)38 gene defines the 5' extent of this promoter in recombinant virus. We have further analyzed this promoter by generating recombinant viruses containing nested deletions 3' of the transcriptional start site and with recombinant viruses containing specific promoter/leader alterations. A recombinant virus containing the U(L)38 promoter/leader from -50 to +9 expressed reporter gene enzyme levels at approximately 10% of those from a recombinant containing the full viral promoter/leader (-50 to +99). The accumulation of reporter gene mRNA in infections with the -50 to +9 recombinant was still regulated with gamma kinetics. Further removal of U(L)38 leader sequences resulted in a nearly complete loss of expression. Analysis of promoter chimera recombinant viruses has shown that sequences downstream of the TATA box and spanning the transcriptional start site of the U(L)38 promoter are functionally distinct from those of either the beta U(L)37 gene or the betagamma VP16 (U(L)48) gene; thus, we conclude that sequences from -31 to +9 of the U(L)38 gene constitute a core gamma promoter. Further deletional and substitutional analyses have also demonstrated the presence of a 14-bp element (the downstream activation sequence) located between +20 to +33 in the nontranslated leader region which is required for full levels of transcription.