Separation of Topoisomerase I Activity from the Regulatory Subunit of Type II CyclicAdenosine Monophosphate-Dependent Protein Kinase

The cAMP-containing phosphoform of the regulatory subunit (Rll) of type II cAMP-dependent protein kinase from rat liver has been reported to have intrinsic DNA topoisomerase Iactivity. We found that highly purified Rll preparations from eight different sources, including rat liver, contained no detectable topoisomerase I activity. Topoisomerase I exhibited an overlapping peak of activity with Rll when rat liver extracts were fractionated by diethylaminoethyl-cellulose chromatography. Topoisomerase I activity was separated from Rll by subsequent cAMP affinity chromatography. The results indicate that the regulatory subunit of cAMP-dependent protein kinase does not contain intrinsic topoisomerase I activity.