Single molecule study of the DNA denaturation phase transition in the force-torsion space

TL;DR

This study uses magnetic tweezers to explore DNA structural transitions in force-torsion space, highlighting denaturation bubbles' role and mapping their formation conditions with a refined theoretical model.

Contribution

The paper introduces an extended model to accurately describe DNA denaturation and fluctuations in force-torsion experiments, providing new insights into DNA behavior under torsional stress.

Findings

Denaturation bubbles form in specific force-torsion regions.

Large fluctuations occur at boundaries where bubbles and plectonemes compete.

The extended model accurately predicts denaturation regions and fluctuations.

Abstract

We use the "magnetic tweezers" technique to reveal the structural transitions that DNA undergoes in the force-torsion space. In particular, we focus on regions corresponding to negative supercoiling. These regions are characterized by the formation of so-called denaturation bubbles, which have an essential role in the replication and transcription of DNA. We experimentally map the region of the force-torsion space where the denaturation takes place. We observe that large fluctuations in DNA extension occur at one of the boundaries of this region, i.e., when the formation of denaturation bubbles and of plectonemes are competing. To describe the experiments, we introduce a suitable extension of the classical model. The model correctly describes the position of the denaturation regions, the transition boundaries, and the measured values of the DNA extension fluctuations.