Ionic effects on the elasticity of single DNA molecules Export

@article{citeulike:1319124, abstract = {We used a force-measuring laser tweezers apparatus to determine the elastic properties of [lambda]-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 A, well below the high-salt "fully neutralized" value of 450-500 A characteristic of DNA in monovalent salt. The ions Mg2+ and Co(NH3)63+, in which the charge is centrally concentrated, yield lower P values than the polyamines putrescine2+ and spermidine3+, 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. 10.1073/pnas.94.12.6185}, author = {Baumann, Christoph G. and Smith, Steven B. and Bloomfield, Victor A. and Bustamante, Carlos}, citeulike-article-id = {1319124}, citeulike-linkout-0 = {http://dx.doi.org/10.1073/pnas.94.12.6185}, citeulike-linkout-1 = {http://www.pnas.org/content/94/12/6185.abstract}, citeulike-linkout-2 = {http://www.pnas.org/content/94/12/6185.full.pdf}, citeulike-linkout-3 = {http://www.pnas.org/cgi/content/abstract/94/12/6185}, citeulike-linkout-4 = {http://view.ncbi.nlm.nih.gov/pubmed/9177192}, citeulike-linkout-5 = {http://www.hubmed.org/display.cgi?uids=9177192}, day = {10}, doi = {10.1073/pnas.94.12.6185}, journal = {PNAS}, keywords = {dna-electrostatics, dna-exp, dna-ions, dna\_bending}, month = {June}, number = {12}, pages = {6185--6190}, posted-at = {2008-11-25 09:17:41}, priority = {3}, title = {Ionic effects on the elasticity of single DNA molecules}, url = {http://dx.doi.org/10.1073/pnas.94.12.6185}, volume = {94}, year = {1997} }

TY - JOUR ID - citeulike:1319124 L3 - citeulike-article-id:1319124 N2 - We used a force-measuring laser tweezers apparatus to determine the elastic properties of [lambda]-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 A, well below the high-salt "fully neutralized" value of 450-500 A characteristic of DNA in monovalent salt. The ions Mg2+ and Co(NH3)63+, in which the charge is centrally concentrated, yield lower P values than the polyamines putrescine2+ and spermidine3+, 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. 10.1073/pnas.94.12.6185 IS - 12 JF - PNAS EP - 6190 TI - Ionic effects on the elasticity of single DNA molecules VL - 94 SP - 6185 KW - dna-electrostatics KW - dna-exp KW - dna-ions KW - dna_bending AU - Baumann, Christoph AU - Smith, Steven AU - Bloomfield, Victor AU - Bustamante, Carlos PY - 1997/06/10/ UR - http://dx.doi.org/10.1073/pnas.94.12.6185 ER -