THE 41-KDA PROTEIN OF HUMAN-HERPESVIRUS-6 SPECIFICALLY BINDS TO VIRAL-DNA POLYMERASE AND GREATLY INCREASES DNA-SYNTHESIS

We previously isolated a 41-kDa early antigen of human herpesvirus 6 ( HHV-6), which exhibited nuclear localization and DNA-binding activity (Agulnick et al., 1993). In this study, we observed that a 110-kDa pro tein was coimmunoprecipitated with p41 from HHV-6-infected cells by an anti-p41 antibody. This 110-kDa protein was identified as the HHV-6 D NA polymerase (Pol-6) by an antibody raised against the N terminus of Pol-6. Reciprocal immunoprecipitation and Western blot analyses confir med that p41 complexes with Pol-6 in HHV-6-infected cells. In addition , both p41 and Pol-6 were expressed in vitro and shown to form a speci fic complex. An in vitro DNA synthesis assay using primed M13 single-s tranded DNA template demonstrated that p41 not only increased the DNA synthesis activity of Pol-6 but also allowed Pol-6 to synthesize DNA p roducts corresponding to full-length M13 template (7249 nucleotides). By contrast, Pol-6 alone could only synthesize DNA of <100 nucleotides . The functional interaction between Pol-6 and p41 appears to be speci fic because they could not be physically or functionally substituted i n vitro by their herpes simplex virus 1 homologues. Moreover, as revea led by mutational analysis, both the N and C termini of Pol-6 contribu te to its binding to p41. In the case of p41, the N terminus is requir ed for increasing DNA synthesis but not binding to pol-6, whereas the C terminus is totally dispensable. (C) 1998 Academic Press.