The N-Terminal Domain of Human Topoisomerase IIα Is a DNA-Dependent ATPase

We have constructed clones encoding N-terminal fragments of human DNA topoisomerase IIα. We show that the N-terminal domain (∼50 kDa) has an intrinsic ATPase activity that can be stimulated by DNA. The enzyme obeys Michaelis−Menten kinetics showing a ∼6-fold increase in k cat in the presence of DNA. Cross-linking studies indicate that the N-terminal domain is a dimer in the absence and presence of nucleotides. Using site-directed mutagenesis, we have identified the catalytic residue for ATP hydrolysis as Glu86. Phosphorylation of the N-terminal domain with protein kinase C does not affect the ATPase activity. The ATPase domain of human topoisomerase IIα shows significant differences from its counterpart in DNA gyrase and we discuss the mechanistic implications of these data.