ASSOCIATION OF ORIGIN-BINDING PROTEIN AND SINGLE-STRAND DNA-BINDING PROTEIN, ICP8, DURING HERPES-SIMPLEX VIRUS TYPE-1 DNA-REPLICATION IN-VIVO

The herpes simplex virus type 1 (HSV-1) origin binding protein (UL9 pr otein) interacts specifically with the HSV-1 encoded single strand DNA binding protein ICP8 (Boehmer, P. E. and Lehman, I. R. (1994) Proc. N atl. Acad. Sci. U.S.A. 90, 8444-8448). A UL9 mutant protein (UL9DM27) that lacks the C-terminal 27 amino acids shows normal origin-specific DNA binding and retains its DNA dependent ATPase and helicase activiti es, but has a greatly reduced affinity for ICP8. The extreme C-termina l portion of the UL9 protein is therefore required for ICP8 binding. T he helicase activity of the UL9DM27 protein is approximately 8-fold gr eater than that of the wild type UL9 protein and is not stimulated by ICP8. The UL9DM27 protein has a reduced ability to replicate origin-co ntaining plasmids in vivo. Consequently, the interaction between the U L9 protein and ICP8 is likely to be important for origin-dependent DNA replication in vivo, presumably to promote efficient unwinding of the DNA at an HSV-1 origin of DNA replication.