Nuclear magnetic resonance signal assignments of purified [13C]methyl-enriched yeast phenylalanine transfer ribonucleic acid.

Yeast tRNA Phe, enriched in carbon-13 specifically at the naturally occurring methyl groups, has been produced through biosynthesis, then purified, and analyzed. Transfer RNA Phe was purified from the [13C]methyl-enriched, unfractionated tRNA that had been extracted from a methionine auxotroph of Saccharomyces cerevisiae [Agris, P. F., Kovacs, S. A. H., Smith, C., Kopper, R. H., & Schmidt, P. G. (1983) Biochemistry 22, 1402-1408]. The yeast had been grown in minimal medium supplemented with [13C]methylmethionine. Transfer RNA Phe purity and the full extent of nucleoside modification were confirmed by high-performance liquid chromatography of constituent nucleosides with simultaneous UV spectral identification and quantitation. Mass spectometry of [13C]methyl-enriched nucleosides and NMR of the tRNA indicated an enrichment of at least 70 atom %. Twelve resolved and prominent carbon-13 NMR signals from the tRNA were seen between 10 and 60 ppm. These have been assigned to 13 of the 14 naturally occurring methyl groups. However, the partially resolved signals assigned to the two 5-methylcytidines could not be assigned to their specific nucleoside positions of either 40 or 49 in the molecule. In addition, the partially resolved signals of the two methyl esters of wybutosine could not be distinguished. The methyl group found not to be enriched with 13C is bound to the ring carbon in the hypermodified nucleoside wybutosine (Y). A 13th enriched signal downfield (120.9 ppm) has been assigned to one of the two carbons added to guanosine to form the third ring in the biosynthesis of Y. The 13C enrichment of this ring carbon demonstrates its origin from the methionine methyl group.(ABSTRACT TRUNCATED AT 250 WORDS)