title: Mono- and trivalent ions around DNA: a small-angle scattering study of competition and interactions.
abstract: The presence of small numbers of multivalent ions in DNA-containing solutions results in strong attractive forces between DNA strands. Despite the biological importance of this interaction, e.g., DNA condensation, its physical origin remains elusive. We carried out a series of experiments to probe interactions between short DNA strands as small numbers of trivalent ions are included in a solution containing DNA and monovalent ions. Using resonant (anomalous) and nonresonant small angle x-ray scattering, we coordinated measurements of the number and distribution of each ion species around the DNA with the onset of attractive forces between DNA strands. DNA-DNA interactions occur as the number of trivalent ions increases. Surprisingly good agreement is found between data and size-corrected numerical Poisson-Boltzmann predictions of ion competition for non- and weakly interacting DNAs. We also obtained an estimate for the minimum number of trivalent ions needed to initiate DNA-DNA attraction.
authors.affiliation: School of Applied and Engineering Physics, Cornell University, Ithaca, New York.
authors.forename: Kurt
authors.initials: K
authors.lastname: Andresen
authors.forename: Xiangyun
authors.initials: X
authors.lastname: Qiu
authors.forename: Suzette A
authors.initials: SA
authors.lastname: Pabit
authors.forename: Jessica S
authors.initials: JS
authors.lastname: Lamb
authors.forename: Hye Yoon
authors.initials: HY
authors.lastname: Park
authors.forename: Lisa W
authors.initials: LW
authors.lastname: Kwok
authors.forename: Lois
authors.initials: L
authors.lastname: Pollack
mesh_terms: D001665:Binding Sites; D003198:Computer Simulation; D004247:DNA / Q000737:chemistry*; D007477:Ions / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D053838:Scattering, Small Angle; D014961:X-Ray Diffraction / Q000379:methods*
chemical_list: D007477:Ions; D004247:DNA