Elongation/Compaction of Giant DNA Caused by Depletion Interaction with a Flexible Polymer

TL;DR

This study investigates how the addition of flexible polymer PEG causes giant DNA to undergo elongation or compaction, revealing phase-dependent structural changes driven by depletion interactions.

Contribution

It demonstrates the phase-dependent conformational changes of giant DNA induced by PEG, highlighting the role of depletion interactions in DNA structural transitions.

Findings

DNA compacts via coil-globule transition at low concentrations

DNA extends through phase segregation at high concentrations

Depletion interaction explains opposite conformational changes

Abstract

Structural changes in giant DNA induced by the addition of the flexible polymer PEG were examined by the method of single-DNA observation. In dilute DNA conditions, individual DNA assumes a compact state via a discrete coil-globule transition, whereas in concentrated solution, DNA molecules exhibit an extended conformation via macroscopic phase segregation. The long axis length of the stretched state in DNA is about 1000 times larger than that of the compact state. Phase segregation at high DNA concentrations occurs at lower PEG concentrations than the compaction at low DNA concentrations. These opposite changes in the conformation of DNA molecule are interpreted in terms of the free energy, including depletion interaction.