MDA-MB-231 cells were treated with increasing concentrations of CuOP for 1 h (under conditions described in section 2.1), genomic DNA (gDNA) immediately isolated, and 1-μg aliquots assayed for DPC using the appropriate antisera. A, Ku antigen; B, PARP1; C, Polλ. For panel D, WT or POLL−/− MEF were treated and assayed for Ku-DPC. For each set of experiments, a representative blot is shown, with quantification for n= 3 independent experiments, normalized to untreated cells. Error bars show +/− S.D. * indicates p<0.05 (two-tailed Student’s t-test) compared to untreated cells.