The Cellular C1 Factor of the Herpes Simplex Virus Enhancer Complex is a Family of Polypeptides

The alpha/immediate early genes of herpes simplex virus are regulated by the specific assembly of a multiprotein enhancer complex containing the Oct-1 POU domain protein, the viral alpha-transinduction factor alpha TIF, (VP16, ICP25), and the C1 cellular factor. The C1 factor from mammalian cells is a heterogeneous but related set of polypeptides that interact directly with the alpha-transinduction factor to form a heteromeric protein complex. The isolation of cDNAs encoding the polypeptides of the C1 factor suggests that these proteins are proteolytic products of a novel precursor. The sequence of the amino termini of these polypeptide products indicate that the proteins are generated by site-specific cleavages within a reiterated 20-amino acid sequence. Although the C1 factor appears to be ubiquitously expressed, it is localized to subnuclear structures in specific cell types.