Nucleotides U28-A42 and A37 in unmodified yeast tRNA(Trp) as negative identity elements for bovine tryptophanyl-tRNA synthetase

Wild-type bovine and yeast tRNAT(Trp) are efficiently aminoacylated by tryp tophanyl-tRNA synthetase both from beef and from yeast. Upon loss of modifi ed bases in the synthetic transcripts, mammalian tRNA(Trp) retains the doub le recognition by the two synthetases, while yeast tRNA(Trp) loses its subs trate properties for the bovine enzyme and is recognised only by the cognat e synthetase. By testing chimeric bovine-yeast transcripts with tryptophany l-tRNA synthetase purified from beef pancreas, the nucleotides responsible for the loss of charging of the synthetic yeast transcript have been locali sed in the anticodon arm. A complete loss of charging akin to that observed with the yeast transcript requires substitution in the bovine backbone of G37 in the anticodon loop with yeast A37 and of C28-G42 in the anticodon st em,vith yeast U2-A42, Since A37 does not prevent aminoacylation of the wild -type yeast tRNA(Trp) by the beef enzyme, a negative combination apparently emerges in the synthetic transcript after unmasking of U28 by loss of pseu dourydilation. (C) 2001 Federation of European Biochemical Societies. Publi shed by Elsevier Science B.V. All rights reserved.