Expression of Y805F:Rad17Δ GFP:Top2 rescues localization of Mre11 and ATM to the bridge DNA next to the midbody in Top2α-depleted cells. (A–C) Localization and mean intensity of ATM at the bridge DNA next to the midbody in BE cells, in the absence (control) or presence of Rad17 siRNA. (D–F) Localization and mean intensity of Aurora B at the midbody ring. Mean ± SD from n cells. Values in control were set to 1. (G) Percentage of broken DNA bridges. Mean ± SD from three independent experiments (n > 120). ***, P < 0.001 (Student’s t test). (H–M) Localization and mean intensity of Mre11 or ATM at the bridge DNA next to the midbody in BE cells expressing siRNA-resistant (R) WT, Y805F, or Y805F:Rad17^Δ GFP:Top2^R in the presence of Top2α siRNA. Mean ± SD from n cells. Values in WT were set to 1. (N) Percentage of broken DNA bridges in cells transfected as in J and M. Mean ± SD. SD from three independent experiments (n > 120). ***, P < 0.001 (ANOVA and Student’s t test). Broken chromatin bridges are indicated by dotted arrows. Arrowheads indicate DNA knots. Midbodies (boxed areas) were re-exported and are shown at higher magnification. Numbers below/next to each bar indicate n. Scale bars, 5 μm.