A protein kinase activity tightly associated with Drosophila type II DNA topoisomerase

A protein kinase activity has been identified that is tightly associated with the purified Drosophila type II DNA topoisomerase. The kinase and topoisomerase activities are not separated when the enzyme is subjected to analytical chromatography (phosphocellulose, single-strand DNA agarose, and Sephacryl S-300) and analytical glycerol gradient sedimentation. These two activities are also inactivated to the same extent by either heat or N-ethylmaleimide treatment. The evidence, however, does not rule out the possibility that the kinase activity resides in a polypeptide other than the topoisomerase polypeptide. The topoisomerase-associated protein kinase activity is not stimulated by Ca2+ or cyclic nucleotides. It shows a broad substrate range, including the DNA topoisomerase itself, casein, phosvitin, and histones. Phosphoamino acid analysis identified phosphoserine and phosphothreonine in polypeptides modified by the topoisomerase-associated protein kinase. No similar activity has been identified previously in Drosophila melanogaster.