Investigation of the Structure of Yeast tRNAPhe by Nuclear Magnetic Resonance: Paramagnetic Rare Earth Ion Probes of Structure

摘要

The binding of paramagnetic rare earth ions to yeast tRNA^Phe shifts some resonances in the low-field nuclear magnetic resonance spectrum that have been assigned to ring nitrogen protons of specific Watson-Crick base pairs. The changes in the nuclear magnetic resonance spectrum as the tRNA is titrated with Eu³⁺ indicate that 4 (or 5) Eu³⁺ ions are tightly bound, that the metal binding is in the fast exchange limit, and that the binding to different sites in the molecule is sequential rather than cooperative. The first metal bound simultaneously shifts resonances associated with the dihydrouridine and the -C-C-A stem. This permits us to conclude that the folding of the tRNA^Phe in solution brings the phosphate backbone of the -C-C-A and the dihydrouridine stems into close proximity. A model of the three-dimensional structure of tRNA^Phe incorporating this new information appears to be compatible with the results obtained from x-ray diffraction.