Dynamics of DNA Supercoils

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Science  13 Sep 2012:
DOI: 10.1126/science.1225810

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DNA in cells exhibits a supercoiled state where the double helix is additionally twisted to form extended intertwined loops called plectonemes. Although supercoiling is vital to many cellular processes, its dynamics remain elusive. Here, we directly visualize the dynamics of individual plectonemes. We observe that multiple plectonemes can be present and that their number depends on applied stretching force and ionic strength. Plectonemes moved along DNA by diffusion or, unexpectedly, by a fast hopping process that facilitated very rapid (<20 ms) long-range plectoneme displacement by nucleating a new plectoneme at a distant position. The observations directly reveal the dynamics of plectonemes and identify a new mode of movement that allows long-distance reorganization of the conformation of the genome on a millisecond time scale.

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