Abstract: The structure of phenylalanine transfer ribonucleic acid (tRNA^Phe) in solution was explored by ¹H nuclear magnetic resonance (¹H NMR) spectroscopy to evaluate the effect of europium ions (Eu³⁺) on the structural and conformational change. Trivalentions Eu³⁺ have specific effects on the iminoproton region of the ¹H NMR spectra of yeast tRNA^Phe. The dependence of the iminoproton spectra of yeast tRNA^Phe as a function of Eu³⁺ concentration was examined, and the results suggested that the tertiary base pair G₁₅·C₄₈, which is located on the terminal in the augmented dihydrouridine helix (D-helix) was markedly affected by Eu³⁺ (shifted downfield by 0.85). Base pair U₈·A₁₄ in yeast tRNA^Phe, which are stacked on G₁₅·C₄₈, was also affected by added Eu³⁺ when 1~2Mg²⁺ ions were also present. Ano ther imino proton that may be affected by Eu³⁺ in yeast tRNA^Phe is that of the tertiary base pair G₁₉·C₅₆. The assignment of this resonance in yeast tRNA^Phe is tentative since it is located in the region of highly overlapping resonances between 12.6 and 12.2. This base pair helps to anchor the D-loop to the TΨC loop. The binding of Eu³⁺ caused conformational change of tRNA, which is responsible for shifts to upfield or downfield in ¹H NMR spectra.

Key words: Europiumion, Transfer ribonucleic acid, NMR