PHOSPHORYLATION OF DNA TOPOISOMERASE-II BY CASEIN KINASE-II - MODULATION OF EUKARYOTIC TOPOISOMERASE-II ACTIVITY INVITRO

The phosphorylation of Drosophila melanogaster DNA topoisomerase II by purified casein kinase II was characterized in vitro. Under the conditions used, the kinase incorporated a maximum of 2-3 molecules of phosphate/homodimer of topoisomerase II. No autophosphorylation of the topoisomerase was observed. The only amino acid residue modified by casein kinase II was serine. Apparent Km and Vmax values for the phosphorylation reaction were 0.4 .mu.M topoisomerase II and 3.3 .mu.mol of phosphate incorporated/min per mg of kinase, respectively. Phosphorylation sitmulated the DNA relaxation activity of topoisomerase II by 3-fold over that of the dephosphorylated enzyme, and the effects of modification could be reversed by treatment with alkaline phosphatase. Posttranslational enzymatic modifications can be used to modulate the interaction between topoisomerase II and DNA.