Abstract. RNA polymerase I preparations purified from a rat hepatoma contained DNA topoisomerase activity. The DNA topoisomerase associated with the polymerase had an Mr of 110000, required Mg2+ but not ATP, and was recognized by anti-topoisomerase I antibodies. When added to RNA polymerase I preparations containing topoisomerase activity, anti-topoisomerase I antibodies were able to inhibit the DNA relaxing activity of the preparation as well as RNA synthesis in vitro. RNA polymerase II prepared by analogous procedures did not contain topoisomerase activity and was not recognized by the antibodies. The topoisomerase I: polymerase I complex was reversibly dissociated by column chromatography on Sephacryl S200 in the presence of 0.25 M (NH 4 hS04. Topoisomerase I was immunolocalized in the transcriptionally active ribosomal gene complex containing RNA polymerase I in situ. These data indicate that topoisomerase I and RNA polymerase I are tightly complexed both in vivo and in vitro, and suggest a role for DNA topoisomerase I in the transcription of ribosomal genes.

SUMMARYIt has been suggested that herpes simplex virus (HSV) type 1 may induce a virusspecific DNA topoisomerase activity which copurifies with virus-induced DNA polymerase. We have examined DNA topoisomerase (TOPO) I and II activities in HSV-2-infected HeLa $3 cells. Both activities were partially purified using DEAEcellulose, phosphocellulose and double-stranded DNA cellulose column chromatography. It was found that both activities could be separated from HSV-2-specific DNA polymerase. Throughout the purification TOPOI could be immunologically detected with a monoclonal antibody developed against human TOPO I. Regardless of the source, mock-or HSV-2-infected human cells, both types of topoisomerase were equally tolerant of 200 mM-KCI. There appeared to be no apparent heterogeneity of TOPOI in HeLa $3 cells through the course of the HSV-2 infection. We conclude that host cell topoisomerases are quite stable in HSV-2-infected HeLa $3 cells and that there is no evidence that HSV-2 is capable of inducing HSV-2-specific TOPO I and TOPO II activities.

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