ASSOCIATION BETWEEN THE P170 FORM OF HUMAN TOPOISOMERASE-II AND PROGENY VIRAL-DNA IN CELLS INFECTED WITH HERPES-SIMPLEX VIRUS TYPE-1

Endogenous host topoisomerase II acts upon herpes simplex virus type 1 (HSV-I) DNA in infected cells (S. N. Ebert, S. S. Shtrom, and M. T. M uller, J. Virol. 56:4059-4066, 1990), and cleavage is directed exclusi vely at progeny viral DNA while parental DNA is resistant. To evaluate the possibility that HSV-1 induces topoisomerase II activity which co uld account for the preferential cleavage of progeny viral DNA, we ass essed topoisomerase II cleavage activity on cellular and viral DNA sub strates before and after the initiation of viral DNA replication. me s how that cleavage of a host gene in meek-infected cells was similar to that observed in HSV-1-infected cells, regardless of whether viral DN A replication had occurred. In addition, quantitative measurements rev ealed comparable amounts of topoisomerase II activity in infected and mock-infected cells; thus, HSV-1 neither induces nor encodes its own t ype II topoisomerase and cleavages in vivo are due to a preexisting ho st topoisomerase. Human cells contain two isozymes of topoisomerase II (p170 and p180), encoded by separate genes. Through the use of isozym e-specific antibodies, we demonstrate that only p170 was found to be c ross-linked to HSV-1 DNA even though both forms were present at nearly constant levels in HSV-1-infected cells. Immunofluorescence revealed that by 6 h postinfection, p170 becomes redistributed and localized to sites of active viral DNA synthesis. The data suggest that p170 gains preferential access to replicated viral DNA molecules, which explains why topoisomerase II activity is concentrated on progeny DNA.