Single-stranded nucleic acid elasticity arises from internal electrostatic tension

TitleSingle-stranded nucleic acid elasticity arises from internal electrostatic tension
Publication TypeJournal Article
Year of Publication2017
AuthorsDR Jacobson, DB McIntosh, MJ Stevens, M Rubinstein, and OA Saleh
JournalProceedings of the National Academy of Sciences of the United States of America
Volume114
Issue20
Start Page5095
Pagination5095 - 5100
Date Published05/2017
Abstract

<jats:p>Understanding of the conformational ensemble of flexible polyelectrolytes, such as single-stranded nucleic acids (ssNAs), is complicated by the interplay of chain backbone entropy and salt-dependent electrostatic repulsions. Molecular elasticity measurements are sensitive probes of the statistical conformation of polymers and have elucidated ssNA conformation at low force, where electrostatic repulsion leads to a strong excluded volume effect, and at high force, where details of the backbone structure become important. Here, we report measurements of ssDNA and ssRNA elasticity in the intermediate-force regime, corresponding to 5- to 100-pN forces and 50–85% extension. These data are explained by a modified wormlike chain model incorporating an internal electrostatic tension. Fits to the elastic data show that the internal tension decreases with salt, from <jats:inline-formula><m:math xmlns:m="http://www.w3.org/1998/Math/MathML" overflow="scroll"><m:mo>&gt;</m:mo></m:math></jats:inline-formula>5 pN under 5 mM ionic strength to near zero at 1 M. This decrease is quantitatively described by an analytical model of electrostatic screening that ascribes to the polymer an effective charge density that is independent of force and salt. Our results thus connect microscopic chain physics to elasticity and structure at intermediate scales and provide a framework for understanding flexible polyelectrolyte elasticity across a broad range of relative extensions.</jats:p>

DOI10.1073/pnas.1701132114
Short TitleProceedings of the National Academy of Sciences of the United States of America