Differentiation and DNA contact points of host proteins binding at the cis site for virion-mediated induction of alpha genes of herpes simplex virus 1.

Transcriptional trans-activation of the five herpes simplex virus 1 alpha genes by the alpha trans-inducing factor requires a cis-acting site (alpha TIC; with the consensus 5'-GyATGnTAATGArATTCyTTGnGGG-3') located in the promoter-regulatory domains of the alpha genes. In DNA band shift assays with nuclear extracts from either mock-infected or infected cells, the DNA fragments containing an alpha TIC sequence from the alpha 0, alpha 4, and alpha 27 genes formed several cellular protein-DNA complexes designated alpha H1, alpha H2, and alpha H3. The host proteins that formed the alpha H2 and alpha H3 complexes were differentiated from those that formed the alpha H1 complex but not from each other by chromatography and specificity of the DNA-binding sites. The alpha H1 proteins protected the alpha TIC sequence of all three genes from DNase I digestion. Methylation of the purines in the sequence 5'-GyATGnTAAT-3' located at the 5' terminus of the alpha TIC sites precluded the binding of alpha H1. The binding site of the alpha H2-alpha H3 proteins in the alpha 27 gene alpha TIC overlapped, in part, with the alpha H1-binding site. The binding of these proteins was precluded by methylation of the purine residues in the sequence 5'-GCCACGTG-3' located at the 3' terminus of the DNase I footprint. The maximum apparent molecular weight of alpha H1 was 110,000, whereas that of alpha H2-alpha H3 was 64,000. A protein designated alpha H2', resembling alpha H2-alpha H3 with respect to molecular weight and chromatographic properties but differing in sequence specificity, bound to a site adjacent to the alpha H1 site in the fragment carrying an alpha TIC sequence of the alpha 4 gene. alpha H1 and alpha H2-alpha H3 or alpha H2' bound concurrently, notwithstanding the apparent overlap in the DNase I footprints.