In Vitro Systems to Analyze HSV Transcript Processing

During lytic virus replication, herpes simplex virus (HSV) exhibits a closely regulated pattern of viral gene expression and of DNA replication, resulting in virion production (1 ). Broadly, HSV genes can be divided into immediate early, early, and late categories based on the kinetics of their expression. The five immediate early genes are expressed in the absence of prior viral protein synthesis although their expression is stimulated by a viral tegument protein. Two immediate early proteins are essential for virus replication in vitro and act at the transcriptional (IE 175) and posttranscriptional (IE63) levels to regulate early and late gene expression. Throughout infection, mRNA is synthesized using cellular RNA poly-merase II, which is modified by the action of an immediate early protein (2 ).