MDA-MB-231 cells were treated with 10 μM CuOP for 1.5 h, with or without MG132 present (under conditions described in section 2.1), and gDNA isolated immediately. Aliquots of gDNA (1μg) were assayed for: A, Ku antigen; B, PARP1; C, Polλ; or D, OGG1. Separate blots of the same samples were also probed for ubiquitin in each experiment. Representative blots are shown, with quantification for n= 3 independent experiments. Error bars show +/−S.D. for n= 3 independent experiments. * indicates p<0.05 (two-tailed Student’s t-test) comparison for CuOP versus CuOP + MG132.