Top, DNA content (n/2n) of exponentially growing yeast cells. First blot: 2D gel electrophoresis of the distribution of Lk topoisomers (Lk) of the YEp13 DNA in cells quenched at 26oC and after shifting the culture to 35oC for 60 min. Second blot: 2D gel electrophoresis of the same samples upon nicking the YEp13 DNA in order to reveal the occurrence of knots (kn). (B) Experiments conducted as in (A) but in scc1-73 yeast cells. Graph: Pkn of YEp13 before and after the inactivation of cohesin. 