Na+ and Mg2+ Ion Effect on the Stability of a Poly I · Poly A · Poly I Triple Helix

✍ Scribed by Victor A. Sorokin; Vladimir A. Valeev; Elena A. Andrus; Galina O. Gladchenko; Yuri P. Blagoi

• Publisher: John Wiley and Sons
• Year: 2004
• Tongue: English
• Weight: 133 KB
• Volume: 4
• Category: Article
• ISSN: 1616-5187
• DOI: 10.1002/mabi.200400007

✦ Synopsis

Abstract

Summary: Differential UV spectroscopy was used to study the temperature dependence of the conformational equilibrium in aqueous poly I · poly A · poly I (A2I) solutions containing Na^+^ (0.1–2 M) and Mg^2+^ (10^−5^–0.005 M) ions. Over the whole range of the studied Na^+^ and Mg^2+^ concentrations, the heating‐induced destruction of the triple A2I helix is actually the A2I → A + I + I (3 → 1) transition. The rise of the transition temperature with increasing Na^+^ and Mg^2+^ contents is well described by Manning's and the “ligand” theories, which makes it possible to estimate the linear charge density on the single‐stranded poly I (ξ = 1.9 ± 0.1) and the Mg^2+^–A2I binding constant (K = 1 250 M^−1^ for the zero degree of binding). An analytical expression has been obtained, which correlates the constants of Mg^2+^ binding to three‐ and single‐stranded polynucleotides (K~3~ and K~1~, respectively) and the linear charge density on them. There are only minor distinctions between the K~3~ values for A2U and A2I because these polynucleotides have similar structures. The difference in the K~1~ values is also slight as single‐stranded poly U, poly I, and poly A have similar conformations.

Dependence of the conformational transition temperatures of two triple helices with changing Mg^2+^ concentration.

imageDependence of the conformational transition temperatures of two triple helices with changing Mg^2+^ concentration.