Trans and cis-BPDE modified 50 bp double stranded oligonucleotides (1 nM) were incubated with different concentrations of Bca UvrA or UvrA + UvrB as indicated in the figure. UvrA and UvrB relative units: 1 = UvrA 2.5 nM, UvrB 62.5 nM. The reaction was performed at 60 °C for 30 min in a 10 μl reaction containing 50 mM Tris-CI, pH7.5, 50 mM KCI, 10 mM MgCI2, 5 mM DTT and 1 mM ATP. The reaction samples were resolved on 4% native polyacylamide gel run with TBE buffer containing 1 mM ATP and 10 mM MgCI2 at 4 °C. The intensities of the resolved bands were quantitated and the average binding ratios of UvrA or UvrA B with trans- or cis-BPDE substrates were calculated. Means ± SD of four independent experiments are plotted.