title: The effect of sodium ion concentration on intrastrand base-pairing in single-stranded DNA.
abstract: The salt-induced formation of duplex structure (primarily hairpin loops) in denatured calf thymus DNA was monitored by measuring the decrease in absorbance at 260 nm as a function of increasing sodium ion concentration. It was found that this process was noncooperative and could be accurately described by the mass-action expression for the reversible formation of a binary complex: single strand (coil) + free sodium ion <==> hairpin (with associated sodium ion). The equilibrium constant for the transition was found to be 6 (M Na+)-1. The extrapolated absorbance at infinite salt concentration represents 11% hyperchromicity, which is one third of the hyperchromicity of denatured DNA in the absence of salt (36%).
authors.affiliation: Division of Toxicology, University of California, San Francisco 94143.
authors.forename: A R
authors.initials: AR
authors.lastname: Wolfe
authors.forename: T
authors.initials: T
authors.lastname: Meehan
mesh_terms: D000818:Animals; D001482:Base Composition; D002417:Cattle; D004277:DNA, Single-Stranded / Q000737:chemistry*; D009690:Nucleic Acid Conformation / Q000187:drug effects*; D009691:Nucleic Acid Denaturation; D012964:Sodium / Q000494:pharmacology*; D013053:Spectrophotometry
chemical_list: D004277:DNA, Single-Stranded; D012964:Sodium