INTERACTIONS OF A SUBASSEMBLY OF THE HERPES-SIMPLEX VIRUS TYPE-1 HELICASE-PRIMASE WITH DNA

The UL5, UL8, and UL52 genes of herpes simplex virus type 1 encode a m ultisubunit assembly that possesses primase, DNA helicase, and DNA-dep endent nucleoside triphosphatase activities. A subassembly consisting of the UL5 and UL52 gene products retains these activities. The nucleo side triphosphatase activity of the UL5/UL52 subassembly is strongly s timulated by both home- and heteropolymeric single-stranded DNA. Doubl e-stranded DNA has little ability to stimulate the ATPase activity. Th e subassembly binds both double and single-stranded DNA. Nucleotides a re not required for DNA-binding. The minimum length of single stranded DNA that is bound and that stimulates enzymatic activity is about 12 nucleotides. The kinetic parameters of the ATPase activity of the suba ssembly are affected by the length of the oligonucleotide coeffector. The K-m decreases as the coeffector length is increased up to a length of about 20 nucleotides and then remains independent of coeffector le ngth. The first order rate constant for ATPase activity exhibits a qua sihyperbolic dependence on the length of the DNA coeffector and is max imal for coeffectors of 20 nucleotides and longer.