Figure 4.

Induction of top1 cleavage complexes by (+)- and (−)-BaP DE-2 in Chinese hamster V79 cells. After treatment (1 μM camptothecin or BaP DE-2 for 1 h), cell lysates were separated by cesium chloride gradients centrifugation. Fractions were collected from the bottom of the tubes (numbered 1–19 at the bottom of the figure). Presence of top1 protein was assayed in each of the gradient fractions by Western blotting with anti-top1 monoclonal antibody. Cellular DNA was contained in fractions 6–9, which correspond to the top1-DNA complexes.