(B) Lanes 1 and 2: negatively supercoiled plasmid (YEp24) and its equilibrium distribution of Lk topoisomers upon its relaxation with Topo I. Lanes 3 and 4: distribution of Lk topoisomers of YEp24 upon its relaxation in lysates of ∆top1 TOP2 yeast cells in absence and after the addition of ICRF-193. Plots compare the relative intensity of individual topoisomers of the Lk distributions in lanes 2, 3 and 4. 