Cation‐induced conformational changes in tRNA molecules

Abstract

AbstractThe uv absorption spectra and melting profiles of an initially ion‐free solution of E. coli unfractionated tRNA are significantly modified by the addition of either Na+, Mg2+, or Mn2+ or of other first‐series transition‐metal ions such as Ni2+, Co2+, and Zn2+. The main effect of the addition of all monovalent or divalent cations examined is an increase of the ordered and stacking stabilized tRNA structure, as revealed by a drop in the absorption near 260 nm, as well as in the 4‐TU absorption region. Sharp differences have, however, been detected in the 290–305‐nm range in the presence of the various ions studied. When transition‐metal ions were added to a tRNA solution, an absorption peak appeared at 294 nm. This effect is interpreted as a perturbation of the electronic structure of the bases due to direct binding of metal ions to the bases. An analysis of the variation in the spectrum as a function of metal concentration and of the thermal melting reversibility in the presence of various metal ions supports the conclusion that while all ions investigated are involved in binding to the phosphate groups of tRNA, transition‐metal ions are also able to bind directly to the bases.