USE OF TRANSDOMINANT MUTANTS OF THE ORIGIN-BINDING PROTEIN (UL9) OF HERPES-SIMPLEX VIRUS TYPE-1 TO DEFINE FUNCTIONAL DOMAINS

UL9, the origin-binding protein of herpes simplex virus type 1, contai ns six sequence motifs conserved in a large superfamily of RNA and DNA helicases. Single-amino-acid substitution mutations in these moths in activate UL9 function in vivo (R Martinez, L. Shao, and S. R Weller, J . Virol. 66:6735-6746, 1992). Overexpression of wild-type UL9 is inhib itory to plaque formation in a transfection assay which measures viral plaque formation by infectious herpes simplex: virus type 1 DNA. Cons tructs containing mutations in motif I, II, or VI exhibit even stronge r inhibitory effects in the same assay and thus can be considered stro ng transdominant inhibitors of plaque formation by the wild-type virus . The transdominant phenotype can be relieved by introducing a second mutation in the DNA-binding domain or by deleting the N-terminal 35 am ino acids of the protein. The inhibitory effects of wild-type UL9 can also be partially relieved by deletion of amino acids 292 to 404. We p ropose that the N-terminal 35 amino acids of UL9 and residues 292 to 4 04 may define new functional domains of the UL9 protein.