title: The stability of polypurine tetraplexes in the presence of mono- and divalent cations.
abstract: As with other guanine-rich sequences, poly[d(GGA)], poly[d(GA)] and poly[d(GAA)] probably form four-stranded or tetraplex structures. Thermal denaturation profiles were measured for these polymers at pH8 in the presence of Na+, NH4+, K+, Cs+, Mg2+, Ca2+ and Ba2+. For poly[d(GA)], Na+, NH4+, K+ stabilize the tetraplex to similar extents and the Tm increases with increasing ionic strength. In contrast the Tms with Mg2+, Ca2+ and Ba2+ are significantly different and reach maxima at about 5mM of cation. The tetraplex from poly [d(GAA)] behaves in a similar manner. Thermal denaturation profiles for poly[d(GGA)] yield transitions whose hyperchromicity depends both on the concentration and nature of the ion. A reversible cooperative transition is not observed at concentrations greater than 0.15M K+, 1mM Ca2+ or 0.3 mM Ba2+ and hysteresis is evident at some concentrations. These results are consistent with the idea that K+ and ions of a similar size can form a coordination complex with the 6-Keto group of eight guanines (G8-DNA). Unlike the tetraplex polymer this G8-DNA does not melt cooperatively.
authors.affiliation: Department of Biochemistry, University of Saskatchewan, Saskatoon, Canada.
authors.forename: J S
authors.initials: JS
authors.lastname: Lee
mesh_terms: D002413:Cations, Divalent; D002414:Cations, Monovalent; D004247:DNA / Q000737:chemistry*; D004355:Drug Stability; D005090:Exodeoxyribonucleases; D046911:Macromolecular Substances; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D011089:Polydeoxyribonucleotides / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D002413:Cations, Divalent; D002414:Cations, Monovalent; D046911:Macromolecular Substances; D011089:Polydeoxyribonucleotides; D004247:DNA; D005090:Exodeoxyribonucleases; C020133:exodeoxyribonuclease III