A dominant-negative herpesvirus protein inhibits intranuclear targeting ofviral proteins: Effects on DNA replication and late gene expression

The d105 dominant-negative mutant form of the herpes simplex virus 1 (HSV-1 ) single-stranded DNA-binding protein, ICP8 (d105 ICPS), inhibits wild-type viral replication, and it blocks both viral DNA replication and late gene transcription, although to different degrees (M, Gao and D. M. Knipe, J. Vi rol. 65:2666-2675, 1991; Y. M, Chen and D, M, Knipe, Virology 221:281-290, 1996), We demonstrate here that this protein is also capable of preventing the formation of intranuclear prereplicative sites and replication compartm ents during HSV infection. We defined three patterns of ICPS localization u sing indirect immunofluorescence staining of HSV-1-infected cells: large re plication compartments, small compartments, and no specific intranuclear lo calization of ICP8. Cells that form large replication compartments replicat e viral DNA and express late genes. Cells that form small replication compa rtments replicate viral DNA but do not express late genes, while cells with out viral replication compartments are incapable of both DNA replication an d late gene expression. The d105 ICPS protein blocks formation of prereplic ative sites and large replication compartments in 80% of infected cells and formation of large replication compartments in the remaining 20% of infect ed cells. The phenotype of d105 suggests a correlation between formation of large replication compartments and late gene expression and a role for int ranuclear rearrangement of viral DNA and bound proteins in activation of la te gene transcription. Thus, these results provide evidence for specialized machinery for late gene expression within replication compartments.