title: Alternative pathways for editing non-cognate amino acids by aminoacyl-tRNA synthetases.
abstract: Evidence is presented that the editing mechanisms of aminoacyl-tRNA synthetase operate by two alternative pathways: pre-transfer, by hydrolysis of the non-cognate aminoacyl adenylate; post-transfer, by hydrolysis of the mischarged tRNA. The methionyl-tRNA synthetases from Escherichia coli and Bacillus stearothermophilus and isoleucyl-tRNA synthetase from E. coli, for example, are shown to reject misactivated homocysteine rapidly by the pre-transfer route. A novel feature of this reaction is that homocysteine thiolactone is formed by the facile cyclisation of the homocysteinyl adenylate. Valyl-tRNA synthetases, on the other hand, reject the more readily activated non-cognate amino acids by primarily the post-transfer route. The features governing the choice of pathway are discussed.
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D000604:Amino Acyl-tRNA Synthetases / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology*; D001411:Geobacillus stearothermophilus / Q000201:enzymology*; D007533:Isoleucine-tRNA Ligase / Q000378:metabolism; D007700:Kinetics; D008718:Methionine-tRNA Ligase / Q000378:metabolism; D010944:Plants / Q000201:enzymology; D013379:Substrate Specificity; D046249:Transfer RNA Aminoacylation; D014637:Valine-tRNA Ligase / Q000378:metabolism
chemical_list: D000596:Amino Acids; D000604:Amino Acyl-tRNA Synthetases; D008718:Methionine-tRNA Ligase; D007533:Isoleucine-tRNA Ligase; D014637:Valine-tRNA Ligase