Short DNA persistence length in a mesoscopic helical model

TL;DR

This study investigates the flexibility of short DNA segments using a mesoscopic helical model, revealing significantly lower persistence lengths than long DNA, indicating intrinsic helix flexibility at short scales due to fluctuations.

Contribution

It introduces a path integral approach to compute short DNA persistence lengths considering twist conformation and sequence effects, highlighting intrinsic flexibility differences from long DNA.

Findings

Short DNA has lower persistence lengths than kilo-base long DNA.

Intrinsic flexibility arises from large fluctuations and local bending.

Sequence heterogeneity influences persistence length through non-linear stacking.

Abstract

The flexibility of short DNA chains is investigated via computation of the average correlation function between dimers which defines the persistence length. Path integration techniques have been applied to confine the phase space available to base pair fluctuations and derive the partition function. The apparent persistence lengths of a set of short chains have been computed as a function of the twist conformation both in the over-twisted and the untwisted regimes, whereby the equilibrium twist is selected by free energy minimization. The obtained values are significantly lower than those generally attributed to kilo-base long DNA. This points to an intrinsic helix flexibility at short length scales, arising from large fluctuational effects and local bending, in line with recent experimental indications. The interplay between helical untwisting and persistence length has been discussed for a heterogeneous fragment by weighing the effects of the sequence specificities through the non-linear stacking potential.