Cellular hypersensitivity of TDP2−/−/− cells to the Top2 poison, etoposide. A, clonogenic survival of TDP2+/+/+, TDP2−/−/+, and TDP2−/−/− (clone 8) cells cultured in the indicated concentrations of etoposide. B, clonogenic survival of TDP2+/+/+ and TDP2−/−/− (clone 93) cells cultured as above. C, clonogenic survival of TDP2+/+/+ cells, TDP2−/−/− cells (clone 8), and pooled populations of TDP2−/−/− (clone 8) transfectants harboring empty expression vector (vector) or expression vector encoding either wild-type human TDP2 (TDP2) or TDP2 with a mutated catalytic domain (TDP2 D262A). Data are the mean ± S.E. of three independent experiments. Where not visible, error bars are smaller than the symbols.