The N-terminal domain of human topoisomerase II alpha is a DNA-dependent ATPase

We have constructed clones encoding N-terminal fragments of human DNA topoi somerase II alpha. We show that the N-terminal domain (similar to 50 kDa) h as an intrinsic ATPase activity that can be stimulated by DNA. The enzyme o beys Michaelis-Menten kinetics showing a similar to 6-fold increase in k(ca t) in the presence of DNA. Cross-linking studies indicate that the N-termin al domain is a dimer in the absence and presence of nucleotides. Using site -directed mutagenesis, we have identified the catalytic residue for ATP hyd rolysis as Glu86. Phosphorylation of the N-terminal domain with protein kin ase C does not affect the ATPase activity. The ATPase domain of human topoi somerase II alpha shows significant differences from its counterpart in DNA gyrase and we discuss the mechanistic implications of these data.