Mutational analysis of the herpes simplex virus trans-inducing factor Vmw65

Vmw65 is a structural component of herpes simplex virus which, in conjunction with host factors, trans-activates the expression of the viral immediate-early genes. In order to examine the relationship between the primary structure of Vmw65 and its trans-activating function, we generated in-frame insertion, deletion, and nonsense mutations in a cloned copy of the gene. The ability of the mutant polypeptides to function as transcriptional activators was assessed by transient transfection of Vero cells using, as the reporter gene, the Escherichia coli chloramphenicol acetyltransferase (cat) gene linked to the promoter-regulatory region from the HSV-1 immediate-early gene coding for Vmw175. These studies have demonstrated that a highly acidic region near the C-terminus of Vmw65 as well as the structural integrity of several other regions of the polypeptide are essential for its transactivating properties, whereas a small region near the N-terminus of the polypeptide is dispensible for activity. Finally, in vivo competition studies using inactive deletion mutants suggest that a domain of the polypeptide located between amino acids 141 and 185 may be involved in protein-protein interactions.