Figure 3.

Induction of top1-mediated DNA cleavage on the DNA strand opposite to a BaP DE-2 adduct and top1-mediated DNA recombination. Oligonucleotides (see Fig. 1B) without (control) or with the trans-S BaP DE-2 adduct (schematic representation at the top of the figure) were 3′-end labeled (asterisks) on the lower strand. Lanes: 1 and 2, DNA alone; 3–7, time course of top1-induced DNA cleavage in the absence of camptothecin; 8–12, same as lanes 3–7 with 10 μM camptothecin (CPT). Reaction times in lanes 3–7 and 8–12 were 15, 30, and 60 min and 2 and 4 h, respectively. The size of the fragments generated by top1 is indicated to the right (see Fig. 5). R, recombination products.