Elasticity and electrostatics of plectonemic DNA

TL;DR

This paper develops a comprehensive 1D continuum model for DNA mechanics that incorporates elasticity and electrostatic interactions, accurately predicting experimental extension-rotation behaviors in single-molecule experiments.

Contribution

It introduces a novel self-contained theory combining elasticity and electrostatics for DNA, applicable to high supercoiling configurations, with predictions validated against experimental data.

Findings

Predicted extension-rotation curves match experimental data.

Identified key parameters like supercoiling radius and torsional stress.

Quantified thermal buckling threshold and linear response slope.

Abstract

We present a self-contained theory for the mechanical response of DNA in single molecule experiments. Our model is based on a 1D continuum description of the DNA molecule and accounts both for its elasticity and for DNA-DNA electrostatic interactions. We consider the classical loading geometry used in experiments where one end of the molecule is attached to a substrate and the other one is pulled by a tensile force and twisted by a given number of turns. We focus on configurations relevant to the limit of a large number of turns, which are made up of two phases, one with linear DNA and the other one with superhelical DNA. The model takes into account thermal fluctuations in the linear phase and electrostatic interactions in the superhelical phase. The values of the torsional stress, of the supercoiling radius and angle, and key features of the experimental extension-rotation curves, namely the slope of the linear region and thermal buckling threshold, are predicted. They are found in good agreement with experimental data.