AMMONIUM ION AT LOW CONCENTRATION STABILIZES THE G-QUADRUPLEX FORMATION BY TELOMERIC SEQUENCE

A synthetic analog of telomeric DNA, d(T(6)G(16)) or d(G(4)T(2)G(4)T(2 )G(4)T(2)G(4)) was found to form G-quadruplex structure in NH4-ion env ironments 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 concentr ations. The multiconformational form of G-tetrad could be identified i n NH4(I) upon heating the sample up to 100 degrees C. Circular dichroi sm spectral studies indicated that on thermally treating the complex N H4(I) ion helps in intramolecular G-tetrad formation over intermolecul ar association, However the G-tetrad structure formed in NH4(I) was fo und to be unstable in the presence of intercalator Actinomycin D or Tb (III) ion. It appears that the ionic radius of NP4(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.