The herpes simplex virus type 1 origin-binding protein interacts specifically with the viral UL8 protein

The products of herpes simplex virus type 1 (HSV-1) genes UL5, UL8 and UL52 form a complex in virus-infected cells that exhibits both DNA helicase and DNA primase activities. UL8 protein was purified from insect cells infected with a recombinant baculovirus and used to generate monoclonal antibodies (MAbs). MAb 0811 was shown to recognize the UL8 protein in both Western blots and immunoprecipitation assays and to co-precipitate the other two proteins in the complex from insect cells triply infected with recombinants expressing the UL5, UL8 and UL52 polypeptides. Experiments performed using extracts from doubly infected cells indicated that UL8 could interact separately with both the UL5 and UL52 proteins. Similar experiments using a recombinant virus that expressed the HSV-1 origin-binding protein (OBP), UL9, demonstrated a direct physical interaction between the helicase-primase complex and OBP which involved the UL8 subunit. The C-terminal DNA-binding domain of OBP is dispensable for this interaction, as evidenced by the ability of MAb 0811 to co-precipitate a truncated UL9 protein, containing only the N-terminal 535 amino acids, with UL8.