title: Abrupt transition from a free, repulsive to a condensed, attractive DNA phase, induced by multivalent polyamine cations.
abstract: We have investigated the energetics of DNA condensation by multivalent polyamine cations. Solution small angle x-ray scattering was used to monitor interactions between short 25 base pair dsDNA strands in the free supernatant DNA phase that coexists with the condensed DNA phase. Interestingly, when tetravalent spermine is used, significant inter-DNA repulsion is observed in the free phase, in contrast with the presumed inter-DNA attraction in the coexisting condensed phase. DNA condensation thus appears to be a discrete, first-order-like, transition from a repulsive gaseous to an attractive condensed solid phase, in accord with the reported all-or-none condensation of giant DNA. We further quantify the electrostatic repulsive potentials in the free DNA phase and estimate the number of additional spermine cations that bind to DNA upon condensation.
authors.affiliation: School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, USA.
authors.forename: Xiangyun
authors.initials: X
authors.lastname: Qiu
authors.forename: Kurt
authors.initials: K
authors.lastname: Andresen
authors.forename: Jessica S
authors.initials: JS
authors.lastname: Lamb
authors.forename: Lisa W
authors.initials: LW
authors.lastname: Kwok
authors.forename: Lois
authors.initials: L
authors.lastname: Pollack
mesh_terms: D002412:Cations / Q000737:chemistry; D004247:DNA / Q000737:chemistry*; D053838:Scattering, Small Angle; D012996:Solutions; D013095:Spermidine / Q000737:chemistry*; D013096:Spermine / Q000737:chemistry*; D013816:Thermodynamics; D014961:X-Ray Diffraction
chemical_list: D002412:Cations; D012996:Solutions; D013096:Spermine; D004247:DNA; D013095:Spermidine