Functional analysis of a herpes simplex virus type 1 promoter: identification of far-upstream regulatory sequences.

We have performed a functional analysis of DNA sequences upstream from the gene for IE mRNA3 of herpes simplex virus type 1. Nucleotide sequences involved in initiation and positive regulation of transcription have been defined by construction of specific deletions in vitro. Transcription was assayed in vivo by microinjection into Xenopus oocytes, or by introduction of plasmid DNA into tissue culture cells and measurement of transient expression. Three functional promoter elements have been defined: i) Sequences between -16 and -37 which are not essential for transcription but are required for accurate initiation. ii) Proximal promoter sequences which are sufficient for transcription initiation in the absence of upstream sequences. iii) Far-upstream promoter sequences (more than 108bp upstream) which increase transcription in oocytes, and contain positive regulatory sequences (-174 to -331) which respond strongly to a factor in the virus inoculum.