Purification and properties of the herpes simplex virus type 1 UL8 protein

The UL8 Subunit of the Heterotrimeric Herpes Simplex Virus Type 1 Helicase-Primase Is Required for the Unwinding of Single Strand DNA-binding Protein (ICP8)-coated DNA Substrates

“…2, A and B, the helicase activity of the UL5/52 subassembly with this substrate was almost indistinguishable from that of the heterotrimeric enzyme. This result is in agreement with earlier reports (14,15). The effect of ICP8 on the helicase action of the UL5/52/8 and UL5/52 proteins could not be tested because of the helix-destabilizing activity of ICP8 on short duplexes under these conditions (24).…”

“…Although the UL8 gene product is essential for HSV-1 DNA replication in vivo, a subassembly consisting of only the 99-kDa UL5 and 114-kDa UL52 gene products was found to be indistinguishable in its DNA-dependent ATPase, DNA helicase, and DNA primase activities from the heterotrimeric enzyme (13,14). It was subsequently observed that the 80-kDa UL8 protein, which lacks enzymatic and DNA binding activities, can stimulate primer synthesis (15)(16). It can also enhance the utilization of primers synthesized by the UL5/52 heterodimer (17).…”

Replication of Herpes Simplex Virus DNA

“…A subassembly that consists of the UL5 and UL52 subunits retains DNA-dependent ATPase, helicase, and primase activities and therefore constitutes the core enzyme (39,40). In contrast, the UL8 protein lacks detectable enzymatic or DNA binding activities (40,41). Under the appropriate conditions of Mg 2ϩ concentration and ionic strength the helicase activity of the helicase-primase can unwind 60 -65 bp/s, a value consistent with the rate of 50 bp/s estimated for the rate of fork movement in vivo during replication of pseudorabies virus, another herpesvirus (42).…”

A functional interaction of ICP8, the herpes simplex virus single-stranded DNA-binding protein, and the helicase-primase complex that is dependent on the presence of the UL8 subunit.

“…Recent work has shown that mutation of the conserved helicase domains of UL5 disrupts helicase activity while preserving primase activity (K. L. Graves-Woodward & S. K. Weller, unpublished observations). While UL8 alone does not bind to nucleic acid (Parry et al, 1993), it has been proposed to function in transport of the UL5\52 subassembly to the nucleus (Calder et al, 1992). Additionally, UL8 forms a complex with the UL9 protein (McLean et al, 1994).…”