a, U2OS cells were treated and probed as indicated. b,c, As (a) except cells stably expressed GFP-RNF8 or GFP-BRCA1/Flag-BARD1; see Supplementary Figs. 9a and 9b for quantifications. d, U2OS cells were treated and probed as indicated; see Supplementary Figs. 9d 10c for quantifications and siRNA efficiencies, respectively. e,f, U2OS cells stably expressing GFP-PIAS1 (e) or RFP-PIAS4 (f) were treated and probed as indicated. g, Model; dashed arrows indicate protein requirements for accumulation, solid arrows indicate target-protein modifications.