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Updated: Apr 21, 2026

Magnetic Tweezers for the Measurement of Twist and Torque
Published on: May 19, 2014
The response of DNA length and twist to changes in ionic strength
1Department of Chemistry and Chemical Biology, Rutgers University, 610 Taylor Road, Piscataway, NJ, 08854-8087.
Abstract:
We examine twist-stretch coupling of unconstrained DNA using polyelectrolyte theory as applied to a line-charge model along with published data on the ionic-strength dependence of the twist angle. We conclude that twist-stretch coupling is negative: environmental changes that stretch free DNA, unconstrained by externally applied pulling or twisting forces, are accompanied by unwinding of the double helix. We also analyze a helical model and conclude that the observed unwinding of the DNA helix when ionic strength is decreased is driven by radial swelling of the helix.
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