title: Critical amount of oligovalent ion binding required for the B-Z transition of poly (dG-m5dC).
abstract: By working at very low Na+ concentrations (1mM and less), the number of bound Mg(2+), cobalt hexamine (3+), and spermine (4+) necessary to induce the B-Z transition of poly (dG-m5dC) has been directly measured. The results show that if as little as 1 cobalt hexamine(3+) or spermine(4+) is bound per 40-50 nucleotides the transition will occur. A greater fraction of bound Mg(2+) is required, 1 bound Mg(2+)/10 nucleotides. The dependence of the transition midpoint concentrations of oligovalent ions on Na+ concentrations suggests that specific ion binding energies, not included in counterion condensation theory, are responsible for the transition.
mesh_terms: D002412:Cations; D055598:Chemical Phenomena; D002621:Chemistry; D002942:Circular Dichroism; D008274:Magnesium; D009690:Nucleic Acid Conformation; D011089:Polydeoxyribonucleotides; D012964:Sodium; D013096:Spermine
chemical_list: D002412:Cations; D011089:Polydeoxyribonucleotides; D013096:Spermine; C029988:poly(dG-m(5)dC).poly(dG-m(5)dC); D012964:Sodium; D008274:Magnesium