A modified uridine in the first position of the anticodon of a minor species of arginine tRNA, the argU gene product, from Escherichia coli

Abstract

The argU (dnaY) gene product, a minor tRNA^Arg, from Escherichia coii has the anticodon N*CU with an unidentified modified nucleoside N* in position 34 [Kiesewetter, S., Fisher, W. & Sprinzl, M. (1987) Nucleic Acids Res. 15, 3184]. In the present study, argU tRNA was purified from E. coli A 19 strain and nucleoside N* was characterized by the TLC and HPLC analyses. Nucleoside N* was found to be different from any naturally occurring modified nucleosides. From unfractionated E. coli tRNA species, nucleoside N* was prepared in an amount sufficient for ¹H‐NMR experiments. By the analyses of one‐dimensional and two‐dimensional NMR spectra, nucleoside N* was suggested to be 5‐methylaminomethyluridine (mnm⁵U), which was confirmed by comparison with a chemically synthesized preparation of mnm⁵U. Thus, the occurrence of mnm⁵U in mature tRNA was found for the first time. Further, the modification of U(34) to mnm⁵U in this tRNA was found to contribute to the strict recognition of two degenerate codons terminating in A and G.