Analysis of factors influencing kinetics of herpes simplex virus transcription utilizing recombinant virus.

The herpes simplex virus type 1 (HSV-1) transcription program is a regulated cascade in which early and late phases of gene expression are separated by viral DNA replication. While promoters controlling expression of transcripts encoding immediate-early proteins contain virus-specific cis-acting elements, these are in the context of cellular promoter elements, and the promoters controlling expression of other viral transcripts contain only cellular cis-acting elements. We had developed and continue to refine a general method for the production of recombinant viruses in which modified promoters can be inserted into nonessential loci within the viral genome through homologous recombination. This approach has been especially useful in defining the features of model promoters of the various kinetic classes. Our work suggests that class-specific differences in promoter architecture are critical factors in the ability of the cellular transcription machinery to form stable preinitiation complexes at various phases of infection and, thus, mediate kinetic class-specific transcription. Early (beta) promoters contain a TATA box and upstream activation elements while sequences downstream of the TATA homology are dispensible for transcription. Late transcripts can be catagorized as either leaky-late (beta gamma) or strict late (gamma) depending on whether they are readily detectable prior to viral DNA replication. Promoters controlling both types are clearly distinct from early ones in that sequences near the transcription start site which resemble consensus mammalian initiator elements are required along with the TATA box and activator elements. Strict late promoters do not contain elements upstream of the TATA box but include what appears to be a class specific element downstream of the transcription start site.