NMR-STUDY OF NITROGEN-15-LABELED ESCHERICHIA-COLI VALINE TRANSFER-RNA

1,3-N-15-Labeled uracil was synthesized chemically and used to prepare labeled Escherichia coli tRNA(Val) biosynthetically. 500-MHz measurements of N-15 and proton chemical shift were obtained, for all uridine and uridine-related bases, by heteronuclear multiple-quantum coherence spectroscopy. All the uracil NH group resonances were assigned and were in agreement with previous proton-only assignments. The temperature dependence of intensities of resonances was used to infer the relative stability of parts of the molecule. The acceptor stem was the least thermally stable structural feature, while the anticodon and T loop were relatively more stable.