Functional modules important for activated expression of early genes of herpes simplex virus type 1 are clustered upstream of the TATA box

Abstract

Functional analysis of two promoters controlling early herpes simplex virus type 1 (HSV-1) transcripts encoding the U(L)37 and U(L)50 (dUTPase) proteins are described in this report. Transcripts expressed under the control of these promoters were found to be expressed early regardless of the position of the transcription unit within the vital genome. Despite this, wt dUTPase mRNA was 6-10 times more abundant than the U(L)37 transcript both in wt and recombinant viruses. This same difference in transcript abundance was seen when a reporter gene (β-galactosidase) was controlled by the two promoters in recombinant viruses in the heterologous glycoprotein C (gC) locus. Thus, both the kinetics and relative abundance of U(L)50 and U(L)37 transcripts are a direct function of their respective promoter regulatory elements. Characterization of mutated U(L)37 and U(L)50 promoters in recombinant viruses showed that the functional modules important for expression from these promoters are concentrated upstream of the transcription start site; however the extent and composition of these modules in terms of the cis-acting elements they contain was different for each. For the U(L)37 promoter, both a HiNF-P factor binding site (-53 to -58 bp) and the TATA homology (-22 to -27) were required for any detectable expression, while an Sp1 binding site at -123 augmented this but was not absolutely required. In contrast, the only functional elements crucial for expression from the U(L)50 promoter were the TATA box (-25 to -31) and an Sp1 binding site at -117 bp relative to the cap site. Despite differences in detail, when the functional architecture of these two early promoters were compared to the extensively characterized HSV-1 thymidine kinase (U(L)23) promoter, class- specific similarities are clearly apparent.