The stability of polypurine tetraplexes in the presence of mono- and divalent cations
Lee, Jeremy S.; Department of Biochemistry, University of SaskatchewanSaskatoon, Saskatchewan, S7N 0W0, Canada
Журнал:
Nucleic Acids Research
Дата:
1990
Аннотация:
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<sup>+</sup> , NH<sub>4</sub><sup>+</sup>, K<sup>+</sup>, Cs<sup>+</sup>, Mg<sup>2+</sup>, Ca<sup>2;+</sup> and Ba<sup>2+</sup>. For poly[d(GA)], Na<sup>+</sup> , NH<sub>4</sub><sup>+</sup>, K<sup>+</sup> stabilize the tetraplex to similar extents and the Tm increases with increasing ionic strength. In contrast the Tms with Mg<sup>2;+</sup>, Ca<sup>2;+</sup> and Ba<sup>2+</sup> 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<sup>+</sup> ,1mM Ca<sup>2+</sup> or 0.3mM Ba<sup>2;+</sup> and hysteresis is evident at some concentrations. These results are consistent with the idea that K<sup>+</sup> and ions of a similar size can form a coordination complex with the 6-Keto group of eight guanines (G<sub>8;</sub>-DNA). Unlike the tetraplex polymer this G<sub>8;</sub>-DNA does not melt cooperatively.
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