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Herpesviridae UL52/UL70 DNA primase Herpes simplex virus type 1 DNA replication in host cells is known to be mediated by seven viral-encoded proteins, three of which form a heterotrimeric DNA helicase-primase complex. This complex consists of UL5, UL8, and UL52 subunits. Heterodimers consisting of UL5 and UL52 have been shown to retain both helicase and primase activities. Nevertheless, UL8 is still essential for replication: though it lacks any DNA binding or catalytic activities, it is involved in the transport of UL5-UL52 and it also interacts with other replication proteins. The molecular mechanisms of the UL5-UL52 catalytic activities are not known. While UL5 is associated with DNA helicase activity and UL52 with DNA primase activity, the helicase activity requires the interaction of UL5 and UL52. It is not known if the primase activity can be maintained by UL52 alone. The region encompassed by residues 610-636 of HSV1 UL52 is thought to contain a divalent metal cation binding motif. Indeed, this region contains several aspartate and glutamate residues that might be involved in divalent cation binding. The biological significance of UL52-UL8 interaction is not known. Yeast two-hybrid analysis together with immunoprecipitation experiments have shown that the HSV1 UL52 region between residues 366-914 is essential for this interaction, while the first 349 N-terminal residues are dispensable. This family also includes protein UL70 from cytomegalovirus (CMV, a subgroup of the Herpesviridae) strains, which, by analogy with UL52, is thought to have DNA primase activity. Indeed, CMV strains also possess a DNA helicase-primase complex, the other subunits being protein UL105 (with known similarity to HSV1 UL5) and protein UL102. |
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