Why is the condensed phase of DNA preferred at higher temperature? DNA compaction in the presence of a multivalent cation

TL;DR

This study investigates how multivalent cations induce DNA compaction and finds that higher temperatures favor the compact DNA state, explained by increased entropy from ionic exchange.

Contribution

It provides experimental evidence that DNA prefers a compact state at higher temperatures in the presence of multivalent cations, highlighting the role of ionic entropy.

Findings

DNA compaction increases with temperature.

Lower monovalent salt concentrations favor DNA folding.

Ionic exchange enhances entropy, stabilizing the compact state.

Abstract

Upon the addition of multivalent cations, a giant DNA chain exhibits a large discrete transition from an elongated coil into a folded compact state. We performed single-chain observation of long DNAs in the presence of a tetravalent cation (spermine), at various temperatures and monovalent salt concentrations. We confirmed that the compact state is preferred at higher temperatures and at lower monovalent salt concentrations. This result is interpreted in terms of an increase in the net translational entropy of small ions due to ionic exchange between higher and lower valence ions.