AMINOACYL-TRANSFER-RNA SYNTHETASES FROM HIGHER EUKARYOTES

This chapter discusses the recent data on higher eukaryotic (mostly mammalian) aminoacyl-tRNA synthetases (aaRSs) in an attempt to illuminate those features of aaRSs that are less well understood at present and that seem to be typical of multicellular species rather than universal for all aaRSs. AaRSs are indispensable for the protein-synthesizing machinery, catalyze two consecutive reactions: activation of carboxylic groups of all natural amino acids and the transfer of activated amino-acid residues to the cognate transfer RNA (tRNA) molecules, leading to the formation of a specific aminoacyl-tRNA. The key role of aaRSs at the preribosomal stage of protein synthesis is well established. Most remarkably, aaRSs play a central role in deciphering the genetic messages, by transforming the nucleotide language into amino-acid language, with high fidelity. This cognition is achieved, by the perfect fit between the enzyme and its substrate tRNA, coupled with efficient negative discrimination of nonsubstrate tRNAs. Moreover, even within aaRSs, exhibiting the same amino-acid specificity, species specificity also manifests itself. For instance, many aaRSs from Escherichia coli that acylate their cognate tRNAs are unable to fulfill this reaction with tRNAs of the same specificity from yeast or mammals. © 1994, Academic Press Inc.