Binding of the virion protein mediating alpha gene induction in herpes simplex virus 1-infected cells to its cis site requires cellular proteins.

In herpes simplex virus 1-infected cells, the transcription of alpha genes, the first set of genes to be expressed, is induced by a virion component, the alpha-trans-induction factor, and requires a cis site. Homologs of the cis site are present in the promoter-regulatory domains of all alpha genes and bind two cellular proteins designated as alpha H1 and alpha H2-alpha H3. We report that alpha-trans-induction factor, synthesized in vitro or present in nuclear extracts of infected cells, forms complexes with viral DNA fragments containing its cis-acting site only in the presence of cellular proteins and only under conditions that also enable the binding of the alpha H1 protein to the DNA. The induction of alpha genes by alpha-trans-induction factor appears, therefore, to be mediated by the interaction of the viral protein with cellular proteins at its cis-acting site.