The herpes simplex virus 1 UL17 gene is required for localization of capsids and major and minor capsid proteins to intranuclear sites where viral DNA is cleaved and packaged

In nuclei of cells infected with herpes simplex virus (HSV), synthesized Viral DNA accumulates as concatamers that are cleaved into genomic lengths and inserted into preformed capsids. Whereas newly replicated DNA and enzymes required for DNA synthesis accumulate in sites of infected cell nuclei termed replication compartments, the intranuclear site of DNA cleavage and packaging is currently controversial. DNA packaging requires the U(L)6, U(L)15, U(L)17, U(L)25, U(L)28, U(L)32, and U(L)33 genes in addition to the major capsid proteins. Using confocal immunofluorescence microscopy, it was observed that in >95% of HEp-2 cells fixed at late times after infection with wild-type HSV-I, capsids, major capsid proteins ICP5 and ICP35, and the U(L)6-encoded minor capsid protein localized in DNA replication compartments These data support the hypothesis that capsid assembly and DNA cleavage/packaging normally occur in HEp-2 cell replication compartments. In contrast, cells infected with a viral mutant lacking functional U(L)17 contained antigenically dense nuclear aggregates that stained with ICP35, ICP5, and capsid specific antibodies: Cells infected with the U(L)17 mutant virus also displayed U(L)6-specific fluorescence in a diffuse pattern at the nuclear periphery in regions not containing ICP35 and ICP5. Displacement of ICP35 from replication compartments was not observed in cells infected with cleavage/packaging mutants lacking U(L)28 and U(L)33. We conclude that the U(L)17 gene is required for correct targeting of capsids and major and minor capsid proteins to the DNA replication compartment of HEp-2 cells and deduce that this targeting reflects one functional role of U(L)17 in viral DNA cleavage and packaging. (C) 1998 Academic Press.