Three trans-acting regulatory proteins of herpes simplex virus modulate immediate-early gene expression in a pathway involving positive and negative feedback regulation

trans-Acting regulatory components of herpes simplex virus were studied in a transient assay system by the analysis of expression of recombinant constructs which contain virus delayed-early (DE) or immediate-early (IE) upstream promoter-regulatory regions linked to the bacterial gene for chloramphenicol acetyltransferase (CAT). These recombinant CAT constructs were cotransfected into Vero cell cultures together with intact genes for the IE175K protein, the IE110K protein, or the late component, Vmw65. We demonstrate specific functional interactions between the trans-acting factors and their appropriate cis-acting regulatory signals. Thus, the IE175K protein stimulated expression only from the DE-CAT constructs, and the late Vmw65 protein stimulated expression only from the IE-CAT construct. Unexpectedly, however, the IE110K protein stimulated expression from both DE- and IE-CAT constructs. Furthermore, the IE175K protein inhibited both basal levels and IE110K- or Vmw65-activated levels of expression from its own promoter-regulatory region in the IE-CAT construct. These results provide direct evidence for a negative autoregulatory role of IE175K protein on its own expression at the transcriptional level and demonstrate differences in functional properties of the IE175K and IE110K proteins, which we speculate may reflect different mechanisms of action of the two proteins.