Herpes simplex virus virion stimulatory protein mRNA leader contains sequence elements which increase both virus-induced transcription and mRNA stability

Abstract

To investigate the role of 5' noncoding leader sequence of herpes simplex virus type 1 (HSV-1) mRNA in infected cells, the promoter for the 65,000-dalton virion stimulatory protein (VSP), a beta-gamma polypeptide, was introduced into plasmids bearing the chloramphenicol acetyltransferase (cat) gene together with various lengths of adjacent viral leader sequences. Plasmids containing longer lengths of leader sequence gave rise to significantly higher levels of CAT enzyme in transfected cells superinfected with HSV-1. RNase T2 protection assays of CAT mRNA showed that transcription was initiated from an authentic viral cap site in all VSP-CAT constructs and that CAT mRNA levels corresponded to CAT enzyme levels. Use of cis-linked simian virus 40 enhancer sequences demonstrated that the effect was virus specific. Constructs containing 12 and 48 base pairs of the VSP mRNA leader gave HSV infection-induced CAT activities intermediate between those of the leaderless construct and the VSP-(+77)-CAT construct. Actinomycin D chase experiments demonstrated that the longest leader sequences increased hybrid CAT mRNA stability at least twofold in infected cells. Cotransfection experiments with a cosmid bearing four virus-specified transcription factors (ICP4, ICP0, ICP27, and VSP-65K) showed that sequences from -3 to +77, with respect to the viral mRNA cap site, also contained signals responsive to transcriptional activation.