The herpes simplex virus 1 U(L)17 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 Vi ral DNA accumulates as concatamers that are cleaved into genomic lengths an d inserted into preformed capsids. Whereas newly replicated DNA and enzymes required for DNA synthesis accumulate in sites of infected cell nuclei ter med replication compartments, the intranuclear site of DNA cleavage and pac kaging 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 obse rved that in >95% of HEp-2 cells fixed at late times after infection with w ild-type HSV-I, capsids, major capsid proteins ICP5 and ICP35, and the U(L) 6-encoded minor capsid protein localized in DNA replication compartments Th ese data support the hypothesis that capsid assembly and DNA cleavage/packa ging normally occur in HEp-2 cell replication compartments. In contrast, ce lls infected with a viral mutant lacking functional U(L)17 contained antige nically dense nuclear aggregates that stained with ICP35, ICP5, and capsid specific antibodies: Cells infected with the U(L)17 mutant virus also displ ayed U(L)6-specific fluorescence in a diffuse pattern at the nuclear periph ery in regions not containing ICP35 and ICP5. Displacement of ICP35 from re plication compartments was not observed in cells infected with cleavage/pac kaging 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 pro teins to the DNA replication compartment of HEp-2 cells and deduce that thi s targeting reflects one functional role of U(L)17 in viral DNA cleavage an d packaging. (C) 1998 Academic Press.