# Overtwisting induces polygonal shapes in bent DNA

## TL;DR

This study combines analytical and simulation approaches to show that overtwisting in DNA minicircles causes them to adopt polygonal shapes due to twist-bend coupling, affecting their elastic properties and experimental analysis.

## Contribution

It demonstrates that twist-bend coupling induces polygonal shapes in overtwisted DNA and reveals that renormalized stiffness constants govern DNA energies, impacting experimental interpretations.

## Key findings

- Overtwisting leads to polygonal DNA shapes.
- Twist-bend coupling causes periodic high and low curvature regions.
- Renormalized stiffness constants, not bare ones, govern DNA energies.

## Abstract

By combining analytical results and simulations of various coarse-grained models we investigate the minimal energy shape of DNA minicircles which are torsionally constrained by an imposed over or undertwist. We show that twist-bend coupling, a cross interaction term discussed in the recent DNA literature, induces minimal energy shapes with a periodic alternance of parts with high and low curvature resembling rounded polygons. We briefly discuss the possible experimental relevance of these findings. We finally show that the twist and bending energies of minicircles are governed by renormalized stiffness constants, not the bare ones. This has important consequences for the analysis of experiments involving circular DNA meant to determine DNA elastic constants.