Discriminator base of tRNA(Asp) is involved in amino acid acceptor activity

Unmodified E. coli tRNA Asp was obtained by in vitro transcription with T7 RNA polymerase from a plasmid carrying a tRNA Asp sequence adjacent to the T7 promoter. The transcript exhibited almost the same level of amino acid acceptor activity as intact tRNA Asp , and the kinetic parameters were also similar. However, substitution of the discriminator base (the fourth base from the 3′-end) markedly affected the amino acid acceptor activity. These results suggest that the discriminator base in tRNA Asp plays an important role in the recognition of aspartyl-tRNA synthetase.