Figure 2.

Calicheamicin γ produces 50% more damage in negatively supercoiled DNA than in positively supercoiled DNA when activated by glutathione. Samples of negatively and positively supercoiled pUC19 were treated with calicheamicin γ and 10 mM glutathione as described in Materials and Methods and gel-resolved plasmid topoisomers were quantified by PhosphorImager analysis of probed gels; representative experimental results are shown in the graph. The average ratio of double-strand breaks in negatively supercoiled DNA to double-strand breaks in positively supercoiled DNA is 1.5 ± 0.1 (n = 5).