(C) Top: 2D gel electrophoresis of the Lk distributions of the YEp13 minichromosome present in the lysates of ∆top1 TOP2 yeast cells before and after the addition of ICRF-193 (see details in Fig EV3). Plots compare the relative intensity of the Lk distributions (divided into ten sections). Bottom: 2D gel electrophoresis of the same samples upon nicking the DNA in order to reveal the occurrence of knots (see details in Fig EV4). The graph shows Pkn of YEp13 (mean ± SD from three independent experiments). P-values (Student's t test): ns, p > 0.05. 