title: The greater negative charge density of DNA in tris-borate buffers does not enhance DNA condensation by multivalent cations.
abstract: As indicated by recent measurements of the electrophoretic free solution mobility, DNA appears to have a greater helical charge density in Tris-borate-EDTA (TBE) buffers than in Tris-acetate-EDTA (TAE) buffers. Since electrostatic forces play a major role in DNA packaging processes, we have investigated the condensation of closed circular plasmid DNA using total intensity and dynamic light scattering in Tris-borate, Tris-acetate, and Tris-cacodylate buffers with cobaltic hexa-amine (III) [Co(NH(3))(3+)(6)]. We find that neither the critical concentration of Co(NH(3))(3+)(6) nor the hydrodynamic radii of the resulting condensates vary significantly in the buffer systems studied here despite the prediction that DNA condensation should occur at significantly lower Co(NH(3))(3+)(6) concentrations in Tris-borate buffers. Assuming a persistence length behavior similar to B-DNA in the presence of multivalent cations, a decrease in the attractive counterion correlation pressure decay length in Tris-borate buffers does not account for our observations. It is possible that the binding of multivalent cations to DNA may hinder borate association with the DNA double helix.
authors.affiliation: Department of Biochemistry, Molecular Biology, and Biophysics University of Minnesota, 1479 Gortner Avenue St. Paul, MN 55108, USA.
authors.forename: J J
authors.initials: JJ
authors.lastname: Schwinefus
authors.forename: V A
authors.initials: VA
authors.lastname: Bloomfield
mesh_terms: D000588:Amines / Q000737:chemistry / Q000494:pharmacology; D000838:Anions / Q000737:chemistry; D001888:Boric Acids / Q000494:pharmacology*; D002021:Buffers; D002412:Cations / Q000737:chemistry / Q000494:pharmacology*; D011232:Chemical Precipitation; D003035:Cobalt / Q000737:chemistry / Q000494:pharmacology; D004247:DNA / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004492:Edetic Acid / Q000494:pharmacology*; D010957:Plasmids / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D012542:Scattering, Radiation; D014325:Tromethamine / Q000494:pharmacology*
chemical_list: D000588:Amines; D000838:Anions; D001888:Boric Acids; D002021:Buffers; D002412:Cations; C069591:Tris-borate-EDTA buffer; D014325:Tromethamine; D003035:Cobalt; D004247:DNA; D004492:Edetic Acid