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Science 22 July 1994:
Vol. 265. no. 5171, pp. 506 - 508
DOI: 10.1126/science.8036491
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Articles

Science, Vol 265, Issue 5171, 506-508
Copyright © 1994 by American Association for the Advancement of Science

articles

Fluctuations and supercoiling of DNA

JF Marko and ED Siggia

Laboratory for Atomic and Solid State Physics, Cornell University, Ithaca, NY 14853-2501.

Frequently, DNA in vivo is organized into loops that are partially underwound and consequently form interwound helical supercoils. Methods from polymer statistical mechanics are used to show how the competition between entropy (thermal fluctuations) and elastic energy determines supercoil radius and pitch, in good agreement with recent experiments and simulations. Supercoil reorganization by means of slithering (reptation) of the DNA along the supercoil is argued to be a slow process. Extension of supercoiled DNA by an applied force shows a number of unexpected features, including coexistence of interwound and helical states.


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