Analysis of the transcript of the herpes simplex virus DNA polymerase gene provides evidence that polymerase expression is inefficient at the level of translation.

We have mapped the termini and determined the relative abundance and ribosome density of the major cytoplasmic transcript of the DNA polymerase (pol) gene of herpes simplex virus type 1. Nuclease protection and primer extension analyses located the 5' end of the major pol transcript at two closely spaced sites 51 and 57 nucleotides to the left of a BamHI site at map position 0.413. S1-sensitive sites corresponding to additional minor transcripts were found to map further upstream within a palindromic sequence that contains a viral replication origin. The major 3' end was found to map 90 nucleotides upstream of a KpnI site at map position 0.439. Quantitative S1 nuclease assays revealed that pol transcripts were nearly as abundant as transcripts encoded by the viral thymidine kinase gene. However, relatively few pol transcripts were found on large polysomes at 5.5 h after infection, when pol transcripts were most abundant. This was in marked contrast to the polyribosome distribution of transcripts from the thymidine kinase gene and the major DNA-binding protein gene. These results and sequence features of the pol transcript suggest that pol expression is regulated, in part, at the level of translation.