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 UL37 and UL50 (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 viral genome. Despite this,wtdUTPase mRNA was 6–10 times more abundant than the UL37 transcript both inwtand 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 UL50 and UL37 transcripts are a direct function of their respective promoter regulatory elements. Characterization of mutated UL37 and UL50 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 thecis-acting elements they contain was different for each. For the UL37 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 UL50 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 (UL23) promoter, class-specific similarities are clearly apparent.