DOI: 10.1073/pnas.94.12.6185. Ionic effects on the elasticity of single DNA molecules

Ionic effects on the elasticity of single DNA molecules

10.1073/pnas.94.12.6185

Crossref journal-article

Proceedings of the National Academy of Sciences

Proceedings of the National Academy of Sciences (341)

Abstract

We used a force-measuring laser tweezers apparatus to determine the elastic properties of λ-bacteriophage DNA as a function of ionic strength and in the presence of multivalent cations. The electrostatic contribution to the persistence length P varied as the inverse of the ionic strength in monovalent salt, as predicted by the standard worm-like polyelectrolyte model. However, ionic strength is not always the dominant variable in determining the elastic properties of DNA. Monovalent and multivalent ions have quite different effects even when present at the same ionic strength. Multivalent ions lead to P values as low as 250–300 Å, well below the high-salt “fully neutralized” value of 450–500 Å characteristic of DNA in monovalent salt. The ions Mg 2+ and Co(NH 3 ) 6 3+ , in which the charge is centrally concentrated, yield lower P values than the polyamines putrescine 2+ and spermidine 3+ , in which the charge is linearly distributed. The elastic stretch modulus, S , and P display opposite trends with ionic strength, in contradiction to predictions of macroscopic elasticity theory. DNA is well described as a worm-like chain at concentrations of trivalent cations capable of inducing condensation, if condensation is prevented by keeping the molecule stretched. A retractile force appears in the presence of multivalent cations at molecular extensions that allow intramolecular contacts, suggesting condensation in stretched DNA occurs by a “thermal ratchet” mechanism.

Bibliography

Baumann, C. G., Smith, S. B., Bloomfield, V. A., & Bustamante, C. (1997). Ionic effects on the elasticity of single DNAâmolecules. Proceedings of the National Academy of Sciences, 94(12), 6185â6190.

Authors 4

Christoph G. Baumann (first)
Steven B. Smith (additional)
Victor A. Bloomfield (additional)
Carlos Bustamante (additional)

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Dates

Type	When
Created	23 years, 1 month ago (July 26, 2002, 10:31 a.m.)
Deposited	3 years, 4 months ago (April 13, 2022, 3:01 p.m.)
Indexed	1 day, 5 hours ago (Sept. 3, 2025, 5:58 a.m.)
Issued	28 years, 2 months ago (June 10, 1997)
Published	28 years, 2 months ago (June 10, 1997)
Published Online	28 years, 2 months ago (June 10, 1997)
Published Print	28 years, 2 months ago (June 10, 1997)

Funders 0

None

BibTeX

@article{Baumann_1997, title={Ionic effects on the elasticity of single DNA molecules}, volume={94}, ISSN={1091-6490}, url={http://dx.doi.org/10.1073/pnas.94.12.6185}, DOI={10.1073/pnas.94.12.6185}, number={12}, journal={Proceedings of the National Academy of Sciences}, publisher={Proceedings of the National Academy of Sciences}, author={Baumann, Christoph G. and Smith, Steven B. and Bloomfield, Victor A. and Bustamante, Carlos}, year={1997}, month=jun, pages={6185–6190} }

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  "abstract": "<jats:p>\n            We used a force-measuring laser tweezers apparatus to determine the elastic properties of \u03bb-bacteriophage DNA as a function of ionic strength and in the presence of multivalent cations. The electrostatic contribution to the persistence length\n            <jats:italic>P</jats:italic>\n            varied as the inverse of the ionic strength in monovalent salt, as predicted by the standard worm-like polyelectrolyte model. However, ionic strength is not always the dominant variable in determining the elastic properties of DNA. Monovalent and multivalent ions have quite different effects even when present at the same ionic strength. Multivalent ions lead to\n            <jats:italic>P</jats:italic>\n            values as low as 250\u2013300 \u212b, well below the high-salt \u201cfully neutralized\u201d value of 450\u2013500 \u212b characteristic of DNA in monovalent salt. The ions Mg\n            <jats:sup>2+</jats:sup>\n            and Co(NH\n            <jats:sub>3</jats:sub>\n            )\n            <jats:sub>6</jats:sub>\n            <jats:sup>3+</jats:sup>\n            , in which the charge is centrally concentrated, yield lower\n            <jats:italic>P</jats:italic>\n            values than the polyamines putrescine\n            <jats:sup>2+</jats:sup>\n            and spermidine\n            <jats:sup>3+</jats:sup>\n            , in which the charge is linearly distributed. The elastic stretch modulus,\n            <jats:italic>S</jats:italic>\n            , and\n            <jats:italic>P</jats:italic>\n            display opposite trends with ionic strength, in contradiction to predictions of macroscopic elasticity theory. DNA is well described as a worm-like chain at concentrations of trivalent cations capable of inducing condensation, if condensation is prevented by keeping the molecule stretched. A retractile force appears in the presence of multivalent cations at molecular extensions that allow intramolecular contacts, suggesting condensation in stretched DNA occurs by a \u201cthermal ratchet\u201d mechanism.\n          </jats:p>",
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