THE UL8 COMPONENT OF THE HERPES-SIMPLEX VIRUS HELICASE-PRIMASE COMPLEX STIMULATES PRIMER SYNTHESIS BY A SUBASSEMBLY OF THE UL5 AND UL52 COMPONENTS

The herpes simplex virus type 1 (HSV) UL5, UL8, and UL52 proteins form a helicase-primase complex in infected cells, Several laboratories ha ve demonstrated that helicase and nucleoside triphosphatase activities of the heterotrimer (UL5/8/52) are indistinguishable from that of a s ubassembly of UL5 and UL52 (UL5/52). Although the UL5/52 subassembly f unctions in coupled primase-polymerase assays on homopolymeric templat es, its activity on natural DNA templates has been reported to require UL8. To determine the role of UL8 in primase assays, the activity of the UL5/52 subassembly was compared to that of the heterotrimer recons tituted by adding UL8 to UL5/52. We detected significant activity of t he UL5/52 subassembly in coupled primase-polymerase and oligoribonucle otide primer synthesis assays on phi X174 and M13 virion DNAs. However the addition of UL8 to UL5/52 stimulated this activity in a dose-depe ndent manner. We demonstrate that stimulation occurred at the level of primer synthesis. UL8 did not affect the amount or size of primers an nealed to template, their utilization by DNA polymerase, or the use of specific initiation sites within the template. In kinetic studies, th e rate of primer synthesis was increased by UL8 but the K-m for phi X1 74 DNA template was unchanged. These results suggest that a function o f the UL8 component of the HSV helicase-primase complex is to increase the efficiency of primer synthesis by UL5/52.