Effect of Zn2+ and temperature on the conformational equilibrium of single-stranded polyA in neutral solutions

Effect of Zn2+ ions on the conformation of polyA in cacodilic buffer at pH 7 was investigated by differential UV spectroscopy (DUV) and by thermal denaturation. The shapes of the DUV spectra and melting curves suggest a transition of polyA into a more ordered "metallized", possibly double-helical conformation at Zn2+ concentrations above 3 x 10(-5) M. A phase diagram of polyA complexes with Zn2+ was constructed for the temperature range from 20 degrees C to 95 degrees C and Zn2+ concentrations between 10(-5) M and 5 x 10(-4) M. It was found that the transition of a single strand into the "metallized" form is possible only if the length of the disordered single-stranded region becomes larger than a certain critical value, ranging between 98% and 78% as the metal concentration increases from 3 x 10(-5) to 5 x 10(-4) M. (C) 2013 Elsevier B.V. All rights reserved.