The DNA-binding properties of the major regulatory protein alpha 4 of herpes simplex viruses.

The transition from the expression of alpha, the first set of five herpes simplex virus genes expressed after infection, to beta and gamma genes, expressed later in infection, requires the participation of infected cell protein 4 (alpha 4), the major viral regulatory protein. The alpha 4 protein is present in complexes formed by proteins extracted from infected cells and viral DNA fragments derived from promoter domains. This report shows that the alpha 4 protein forms specific complexes with DNA fragments derived from 5' transcribed noncoding domains of late (gamma 2) genes whose expression requires viral DNA synthesis as well as functional alpha 4 protein. Some of the DNA fragments to which alpha 4 binds do not contain homologs of the previously reported DNA binding site consensus sequence, suggesting that alpha 4 may recognize and interact with more than one type of DNA binding site. The alpha 4 proteins can bind to DNA directly. A posttranslationally modified form of the alpha 4 protein designated alpha 4c differs from the alpha 4a and alpha 4b forms with respect to its affinity for DNA fragments differing in the nucleotide sequences of the binding sites.