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. 1998 May 12;95(10):5521–5526. doi: 10.1073/pnas.95.10.5521

Figure 2.

Figure 2

DNA supercoiling of extrachromosomal rings. rKWD50N was produced by excision from either HMR in strains THC10 (SIR) and THC9 (sir3) or from LYS2 in strains THC17 (SIR) and THC16 (sir3). Topoisomers were resolved by electrophoresis in buffer containing chloroquine diphosphate. Autoradiograms were cropped to show DNA rings exclusively. Gaussian centers of the topoisomer distributions are marked with a triangle. The SIR3-dependent shift in linking number was 1.1 ± 0.1 for the ring from HMR but negligible for the ring from LYS2 (based on four independent measurements). The linking number difference between rings from LYS2 and from the derepressed HMR locus was also negligible. A slight increase in mobility in topoisomers from LYS2 arose from four additional bases in the excision cassette (see Materials and Methods).