Torque determination on DNA with magnetic tweezers

TL;DR

This paper introduces a simple method to determine the torque on DNA using magnetic tweezers, enabling measurements at lower forces and providing insights into DNA's torsional properties under different conditions.

Contribution

The study presents a novel, straightforward approach to measure DNA torque that extends the force range of previous methods and estimates key torsional parameters.

Findings

Effective torsional modulus decreases with force

Buckling torque varies with force and salt conditions

Method aligns with high-force measurements at lower forces

Abstract

We deduced the torque applied on a single stretched and twisted DNA by integrating with respect to force the change in the molecule's extension as it is coiled. While consistent with previous direct measurements of the torque at high forces (F>1 pN) this method, which is simple and does not require a sophisticated set-up, allows for lower force estimates. We used this approach to deduce the effective torsional modulus of DNA, which decreases with force and to estimate the buckling torque of DNA as a function of force in various salt conditions.