(F) Top: 2D gel electrophoresis of the Lk distributions of the YEp13 minichromosome produced in the presence of TOP2 or Top2-∆83. 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. Graph: Pkn of YEp13 (mean ± SD from three independent experiments). 