Metabolism of D-aminoacyl-tRNAs in Escherichia coli and Saccharomyces cerevisiae cells

In Escherichia coil, tyrosyl-tRNA synthetase is known to esterify tRNA(Tyr) with tyrosine. Resulting D-Tyr-tRNA(Tyr) can be hydrolyzed by a D-Tyr-tRNA (Tyr) deacylase, By monitoring E. coil growth in liquid medium, we systemat ically searched for other D-amino acids, the toxicity of which might be exa cerbated by the inactivation of the gene encoding D-Tyr-tRNA(Tyr) deacylase , In addition to the already documented case of D-tyrosine, positive respon ses were obtained with D-tryptophan, D-aspartate, D-serine, and D-glutamine . In agreement with this observation, production of D-Asp-tRNA(Asp) and D-T rp-tRNA(Typ) by aspartyl-tRNA synthetase and tryptophanyl-tRNA synthetase, respectively, was established in vitro. Furthermore, the two D-aminoacylate d tRNAs behaved as substrates of purified E. coil D-Tyr-tRNA(Tyr) deacylase . These results indicate that an unexpected high number of D-amino acids ca n impair the bacterium growth through the accumulation of D-aminoacyl-tRNA( Tyr) molecules and that D-Tyr-tRNA(Tyr) deacylase has a specificity broad e nough to recycle any of these molecules. The same strategy of screening was applied using Saccharomyces cerevisiae, the tyrosyl-tRNA synthetase of whi ch also produces D-Tyr-tRNA(Tyr), and which, like E. coil, possesses a D-Ty r-tRNATyr deacylase activity. In this case, inhibition of growth by the var ious 19 D-amino acids was followed on solid medium. Two isogenic strains co ntaining or not the deacylase were compared. Toxic effects of D-tyrosine an d D-leucine were reinforced upon deprivation of the deacylase, This observa tion suggests that, in yeast, at least two D-amino acids succeed in being t ransferred onto tRNAs and that, like in E. coli, the resulting two D-aminoa cyl-tRNAs are substrates of a same D-aminoacyl-tRNA deacylase.