NMR study of the modified base resonances of tRNA tyr- coli

220MHz NMR spectra at 28° show several resolved resonances in the high field region for D₂O solutions of tyrosine specific tRNA from E. coli. These resonances are tentatively identified as arising from protons of the modified nucleoside, 2-methylthio-N⁶-(Δ²-isopentenyl)-adenosine and from the modified guanosine of unknown structure in the “wobble position” of the anti codon loop. Assignment of resonances was aided by comparison with spectra of tRNA_su⁺III^tyr, Form II, whose sequence is closely homologous to tRNA_coli^tyr, except for changes in some modified bases. Line widths of resolved resonances indicate that, at 28°, the methyl groups of modified nucleosides are not completely restricted in their motion relative to the overall motion of the macromolecule.