Transcriptional regulation of a herpes simplex virus immediate early gene is mediated through an enhancer-type sequence.

An enhancer-type sequence has been identified in the promoter region for the herpes simplex virus type 1 (HSV-1) immediate early (IE) mRNA 3. The enhancer-type activity is host cell dependent, being greater in human cells and Syrian hamster cells (the usual host cell for in vitro propagation of HSV) than in Chinese hamster or mouse cells. Enhancer activity is stimulated up to 10-fold after superinfection by tsK, a temperature-sensitive mutant of HSV-1. The induction of enhancer activity is independent of de novo protein synthesis, showing that trans-activation is effected by a component of the virion. We propose that trans-regulation of IE mRNA 3 is mediated through an enhancer-type sequence, and that this provides one explanation for previously described regulation of HSV IE mRNAs by virion components.