IDENTITY ELEMENTS OF TRANSFER RNA(TRP) - IDENTIFICATION AND EVOLUTIONARY CONSERVATION

In this study, the varying reactivities of Bacillus subtilis tryptopha nyl-tRNA synthetase toward prokaryotic, eukaryotic, and halophile tRNA s were employed to define the potential identity elements on tRNA(TrP) . On this basis mutagenesis was performed to obtain, through in vivo h eterologous expression in Escherichia coli and in vitro transcription with T7 RNA polymerase, mutant B. subtilis tRNA(Trp) for comparison wi th the wild-type. These comparisons served to establish G73 and the an ticodon as major identity elements, and A1-U72, G5-C68, and A9 as mino r identity elements. While the tryptophanyl-tRNA synthetase from B. su btilis and E. coli require G73 to function, replacement of G73 by A73 favors the enzyme from yeast. This change points to the variation of t he identity elements for the same amino acid among different organisms . The similarity in these elements between B. subtilis and E. coli try ptophanyl-tRNA synthetase, however, suggests that identity elements on tRNA, like the active centers on enzymes, undergo evolutionary change at slower rates than less essential portions of the macromolecule.