Figure 6.

Covalent poisons inactivate human topoisomerase IIα enzymes when incubated with the protein prior to the addition of DNA. The DNA cleavage activities of wild-type human topoisomerase IIα (black), the catalytic core (red), and hTop2αΔ1175 (blue) were monitored in the presence of 50 μM benzoquinone (left) or 50 μM thymoquinone (right). DNA cleavage levels were calculated relative to cleavage levels induced when the drug and the enzyme were not incubated prior to DNA addition. Error bars represent the standard deviation of at least three independent experiments.