Ammonium ion at low concentration stabilizes the G-quadruplex formation by telomeric sequence

Abstract

A synthetic analog of telomeric DNA, d(T₆G₁₆) or d(G₄T₂G₄T₂G₄T₂G₄) was found to form G-quadruplex structure in NH₄-ion environments as low as 1 mM. Other counter ions like K(I) or Sr(II) known to have a stabilizing effect on G-tetrad require much higher concentrations. The multiconformational form of G-tetrad could be identified in NH₄(I) upon heating the sample up to 100° C. Circular dichroism spectral studies indicated that on thermally treating the complex NH₄(I) ion helps in intramolecular G-tetrad formation over intermolecular association. However the G-tetrad structure formed in NH₄(I) was found to be unstable in the presence of intercalator Actinomycin D or Tb(III) ion. It appears that the ionic radius of NH₄(I) influences tight fitting of this ion inside the cavity of the tetrad. The stability of G-tetrad in the presence of very low concentration of NH₄(I) may have potential applications in future.