Transcriptional control of herpesvirus gene expression: Gene functions required for positive and negative regulation

Abstract

We have used an in vitro nuclear run-off assay to measure the levels of transcription of specific herpes simplex virus genes at different times during a lytic infection. We analyzed the effects of inhibition of DNA replication and of defects in two herpes simplex virus regulatory proteins on the transcription of these genes. We present evidence that the transcription of the αICP4 gene is negatively regulated during a lytic infection. The regulation of ICP4 gene transcription requires the β protein ICP8 (where ICP = infected cell polypeptide). Transcription of the βICP8, γ1ICP5, and γ2 glycoprotein C (gC) genes was dependent on ICP4, and transcription of the γ2gC gene was strongly inhibited when DNA replication was blocked. Defects in ICP8 also resulted in increased levels of transcription of the ICP4, ICP8, ICP5, and gC genes from parental viral genomes. Our results suggest that ICP8 may be important in maintaining the highly ordered cascade of viral gene expression.