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Torque and buckling in stretched intertwined double-helix DNAs

Sumitabha Brahmachari, John F. Marko
doi: https://doi.org/10.1101/135905
Sumitabha Brahmachari
1Department of Physics and Astronomy, Northwestern University, Evanston Illinois 60208, USA
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John F. Marko
1Department of Physics and Astronomy, Northwestern University, Evanston Illinois 60208, USA
2Department of Molecular Biosciences, Northwestern University, Evanston Illinois 60208, USA
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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 to 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.

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The copyright holder for this preprint is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under a CC-BY-NC 4.0 International license.
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Posted May 09, 2017.
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Torque and buckling in stretched intertwined double-helix DNAs
Sumitabha Brahmachari, John F. Marko
bioRxiv 135905; doi: https://doi.org/10.1101/135905
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Torque and buckling in stretched intertwined double-helix DNAs
Sumitabha Brahmachari, John F. Marko
bioRxiv 135905; doi: https://doi.org/10.1101/135905

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