Regulation of HSV transcription

Herpes simplex virus (HSV) transcripts share many features with both cellular mRNA and the mRNAs expressed by other nuclear-replicating DNA viruses: they are capped, polyadenylated, and generally have an approximately 150 base leader between the cap and translation initiation codon. Further, certain sequence features around individual transcription units are shared: HSV promoters contain TATA and often CATC boxes, and the sequence signal indicating a polyadenylation site (AATAAAA) is standard. In spite of these similarities, there is one very distinct difference between the structure of HSV transcription units and those of other nuclear replicating DNA viruses. Each HSV transcript appears to be controlled by its own promoter and encodes a specific polypeptide. Further, the high degree of splicing seen with most eukaryotic and viral mRNAs is not seen in HSV. Certainly, HSV and other herpesviruses do express some spliced transcripts, but these are in the minority (with HSV at least). Thus a whole hierarchy of potential control points utilized in eukaryotic gene expression is missing or rarely utilized in HSV. Despite this, the high density of gene packaging and relatively complex arrangement of partially overlapping transcripts is seen in HSV transcription as it is in other, smaller DNA viruses.