DNA loop statistics and torsional modulus

TL;DR

This paper introduces a unified model for DNA mechanics that resolves discrepancies in torsional modulus estimates by accounting for writhe effects through simulations and analytic calculations, eliminating the need for cut-offs.

Contribution

It presents a new approach to model DNA loop statistics that unifies existing models and accurately determines the torsional modulus without arbitrary cut-offs.

Findings

Writhe from DNA loops causes discrepancies in torsional modulus estimates.

The proposed model aligns analytical and numerical approaches.

The torsional modulus can be computed without cut-offs using the new method.

Abstract

The modelling of DNA mechanics under external constraints is discussed. Two analytical models are widely known, but disagree for instance on the value of the torsional modulus. The origin of this embarassing situation is located in the concept of writhe. This letter presents a unified model for DNA establishing a relation between the different approaches. I show that the writhe created by the loops of DNA is at the origin of the discrepancy. To take this into account, I propose a new treatment of loop statistics based on numerical simulations using the most general formula for the writhe, and on analytic calculations with only one fit parameter. One can then compute the value of the torsional modulus of DNA without the need of any cut-off.