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Phys Rev E. 2017 May;95(5-1):052401. doi: 10.1103/PhysRevE.95.052401. Epub 2017 May 1.

Torque and buckling in stretched intertwined double-helix DNAs.

Author information

1
Department of Physics and Astronomy, Northwestern University, Evanston, Illinois 60208, USA.
2
Department of Molecular Biosciences, Northwestern University, Evanston, Illinois 60208, USA.

Abstract

We present a statistical-mechanical model for the behavior of intertwined DNAs, with a focus on their torque and extension as a function of their catenation (linking) number and applied force, as studied in magnetic tweezers experiments. Our model produces results in good agreement with available experimental data and predicts a catenation-dependent effective twist modulus distinct from what is observed for twisted individual double-helix DNAs. We find that buckling occurs near the point where experiments have observed a kink in the extension versus linking number, and that the subsequent "supercoiled braid" state corresponds to a proliferation of multiple small plectoneme structures. We predict a discontinuity in extension at the buckling transition corresponding to nucleation of the first plectoneme domain. We also find that buckling occurs for lower linking number at lower salt; the opposite trend is observed for supercoiled single DNAs.

PMID:
28618488
PMCID:
PMC5505651
DOI:
10.1103/PhysRevE.95.052401
[Indexed for MEDLINE]
Free PMC Article

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