title: Counterion-induced condesation of deoxyribonucleic acid. a light-scattering study.
abstract: The addition of the trivalent or tetravalent cations spermidine or spermine to a solution of T7 DNA in aqueous solution causes an alteration of the DNA from its extended coil form to a condensed form. If performed at low DNA concentration and at low ionic strengths, this transformation results in a monomolecular collapse to form a particle with a hydrodynamic radius of about 500 A. We have monitored this change using quasielastic and total intensity light scattering. In a solution of 50% methanol in water, the divalent cations Mg2+ and putrescine also can cause the condensation of DNA. Using Manning's (1978) counterion condensation theory, we calculate a striking unity among these disparate ions: the collapse occurs in each case when from 89 to 90% of the DNA phosphate charges are neutralized by condensed counterions.
mesh_terms: D055598:Chemical Phenomena; D002621:Chemistry; D003090:Coliphages; D004279:DNA, Viral / Q000528:radiation effects*; D008027:Light; D008433:Mathematics; D009690:Nucleic Acid Conformation; D011700:Putrescine; D012542:Scattering, Radiation; D013095:Spermidine; D013096:Spermine
chemical_list: D004279:DNA, Viral; D013096:Spermine; D013095:Spermidine; D011700:Putrescine