The catalytic subunit of the DNA polymerase of herpes simplex virus type 1 interacts specifically with the C terminus of the UL8 component of the viral helicase-primase complex

The herpes simplex virus type 1 (HSV-1) UL8 DNA replication protein is a component of a trimeric helicase-primase complex, Sixteen UL8-specific monoclonal antibodies (MAbs) were isolated and characterized, In initial immunoprecipitation experiments, one of these, MAb 804, was shown to coprecipitate POL, the catalytic subunit of the HSV-1 DNA polymerase, from extracts of insect cells infected with recombinant baculoviruses expressing the POL and UL8 proteins, Coprecipitation of POL was dependent on the presence of UL8 protein, Rapid enzyme-linked immunosorbent assays (ELISAs), in which one protein was bound to microtiter wells and binding of the other protein was detected with a UL8- or POL-specific MAb, were developed to investigate further the interaction between the two proteins, When tested in the ELISAs, five of the UL8-specific MAbs consistently inhibited the interaction, raising the possibility that these antibodies act by binding to epitopes at or near a site(s) on UL8 involved in its interaction with POL, The epitopes recognized by four of the inhibitory, MAbs were approximately located by using a series of truncated UL8 proteins expressed in mammalian cells, Three of these MAbs recognized an epitope near the C terminus of UL8, which was subjected to fine mapping with a series of overlapping peptides, The C-terminal peptides were then tested in the ELISA for their ability to inhibit the POL-UL8 interaction: the most potent exhibited a 50% inhibitory concentration of approximately 5 mu M. Our findings suggest that the UL8 protein may be involved in recruiting HSV-1 DNA polymerase into the viral DNA replication complex and also identify a potential new target for antiviral therapy.