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.