Mapping of functional and antigenic domains of the alpha 4 protein of herpes simplex virus 1

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Abstract
Monoclonal antibodies to .alpha.4, the major regulatory protein of herpes simplex virus 1, have been shown to differ in their effects on the binding of the protein to its DNA-binding site in the promoter-regulatory domain of an .alpha. gene. To map the epitopes, we expressed truncated genes in transient expression systems. All 10 monoclonal antibodies tested reacted with the N-terminal 288-amino-acid polypeptide. To map the epitopes more precisely, 29 15-mer oligopeptides, overlapping by five amino acids at each end, were synthesized and reacted with the monoclonal antibodies. The nine reactive monoclonal antibodies were mapped to seven sites. Of the two monoclonal antibodies which blocked the binding of .alpha.4 to DNA, one (H950) reacted with oligopeptide no. 3 near the N terminal of the protein, whereas the second (H942) reacted with oligopeptide no. 23 near the C terminus of the 288-amino acid polypeptide. In further tests, oligopeptide no. 19 was found to compete with two host proteins, designated as .alpha.H1 and .alpha.H2-.alpha.H3, for binding to DNA as well as to retard DNA in a band shift assay, whereas oligopeptides no. 26, 27, and 28 enhanced the binding of .alpha.4 to DNA. Moreover, oligopeptide no. 27 was also found to retard DNA in a band shift assay. Polypeptide no. 19 competed with .alpha.4 for binding to DNA, whereas no. 27 neither enhanced nor competed with the binding of the host polypeptide .alpha.H1 to its binding site in the promoter-regulatory domain of an .alpha. gene, but did enhance the binding of the .alpha.H2-.alpha.H3 protein to its binding site. In contrast to these results, the truncated .alpha.4 polypeptide, 825 amino acids long, bound to the viral DNA, whereas a shorter, 519-amino-acid-long, truncated polypeptide did not. The 825-amino-acid polypeptide was previously shown to induce in transient expression systems the expression of a late (.gamma.2) viral gene.