(a) IB with cell lysates prepared from cells treated with siRNAs as indicated. (b) Representative images of 53BP1 (upper panel) or BRCA1 (lower panel) at mCherry-LacI-FokI-induced DSBs in cells transfected with the indicated siRNA. Scale bar, 10 μm. (c), Quantification of relative mean fluorescence intensity (RMFI) from b. RMFI was calculated from 200 cells and 3 independent experiments. Error bars represent S.E.M. * indicates p<0.05, ** p<0.005. (d), IB with cell lysates prepared from TIP60-GFP expressing cells treated with siRNAs as indicated. (e) Representative images of BRCA1 and 53BP1 co-staining following fixation at 5 hours after 2 Gy IR treatment of U2OS cells that were transfected with the indicated siRNA. Scale bar, 10 μm. (f) Quantification of percentage of cells possessing greater than 5 BRCA1 IRIF per cell from e. Error bars represent S.E.M. ** indicates p<0.005.