Induction and repression of cellular gene transcription during Herpes simplex virus infection are mediated by different viral immediate‐early gene products

Nuclear run‐off and pulse‐labelling techniques have been used to study the changes in transcription rates of a number of cellular genes during infection with Herpes simplex virus. The majority of these genes show a decrease in transcription rate to about 60% of that observed prior to infection. In contrast, a small number of genes are transcriptionally activated during infection. These effects, which occur at a point in infection after the synthesis of viral proteins but prior to the onset of viral DNA synthesis, are mediated by different immediate‐early proteins of the virus. Thus we show that, whilst transcriptional activation requires a functional ICP4 protein, repression is dependent upon the presence of another immediate early protein‐ICP22.