EFFECT OF Mg^2+ ON DOUBLE AND TRIPLE HELLX FORMATIONS BETWEEN POLY(dA) AND POLY(dT)
Abstract
The Mg2+ ion effect on conformational transitions in double- and triple-helical structures formed by poly(dA) with poly(dT) has been studied in 10 mM cacodylate buffer, pH 7, containing 0.1 M Na+. The investigations were carried out by the method of thermal denaturation using UV absorbance and Rayleigh light scattering detections of melting transitions. Temperatures of helix-to-coil transition of poIy(dA)-poly(dT) and triplex-to-duplex of poly(dA)-2poly(dT) increase linearly with log[Mg2+] and more quickly in the last case that results in superposition of these transitions at [Mg2+]>15 mM. At [Mg2+] > 20 mM during the melting of the both structures aggregation was observed, which arised, according to Bloomfield and co-workers, due to formation of cross-links by Mg2+ ions bridges between partially unplaited polymer strands and disappeared after the end of melting. It is established that at the presence of 0.1 M NaCl magnesium ions do not induce the partial formation of the triplex structure in poly(dA)poly(dT) (disproportionation) as is postulated by other authors in some papers.
KEY WORDS: polynucleotides, double and triple helices, magnesium ions, helix-to-coil transitions, Rayleigh scattering
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