A single base substitution in the variable pocket of yeast tRNA(Arg) eliminates species-specific aminoacylation

Early biochemical data showed that aminoacyl-tRNA synthetases often display ed species-specific recognition of tRNA. We compared the ability of purifie d Saccharomyces cerevisiae and Escherichia coli arginyl-tRNA synthetases to aminoacylate native and transcribed yeast tRNA(Arg) as well as E. coli tRN A(Arg). The kinetic data revealed that yeast ArgRS could charge E. coli tRN A(Arg) but at a lower efficiency than it charged either the transcribed or native yeast tRNA(Arg). E. coli ArgRS can acylate only its cognate E. coli tRNA. Strikingly, a single base change from C to A at position 20 in yeast tRNA(3)(Arg) altered the species specificity. The transcript of yeast tRNA( 3)(Arg) mutant was aminoacylated by E, col ArgRS with a 10(6) increase in k (cat)/K-m over that for aminoacylation of yeast tRNA(3)(Arg) transcript. Th is indicates that A20 is not only an important identity of E. coli tRNA(Arg ), but is also the key to altering species-specific aminoacylation of yeast tRNAArg. (C) 1999 Elsevier Science B.V. All rights reserved.