title: Hydrolytic action of aminoacyl-tRNA synthetases from baker's yeast. "Chemical proofreading" of Thr-tRNA Val by valyl-tRNA synthetase studied with modified tRNA Val and amino acid analogues.
abstract: The properties of native and of two modified tRNA Val species in the correction of misactivated threonine by valyl-tRNA synthetase have been studied. Whereas Thr-tRNA Val-C-C-A could not be isolated in the valyl-tRNA synthetase catalyzed reaction, Thr-tRNA Val-C-C-3'dA is isolable in up to 50% yield in this system and tRNA Val-C-C-3'NH2A is fully aminoacylated with threonine by the same enzyme. The hydrolysis of preformed Thr-tRNA Val-C-C-A by free valyl-tRNA synthetase is 30 times faster than the corresponding breakdown of Val-tRNA Val-C-C-A. This hydrolytic activity is also observed with Thr-tRNA Val-C-C-3'dA although the rate is reduce to that of the reaction of Val-tRNA Val-C-C-A. Modification of the threonine to O-methylthreonine, which is also a substrate for valyl-tRNA synthetase, leads to stabilization of the O-methylthreonyl-tRNA esters. The AMP/PP independent hydrolysis under aminoacylating conditions, which is a measure of the correction process, indicates that O-MeThr-tRNA Val-C-C-A is only very slowly corrected while the tRNA Val-C-C-3'dA and tRNA Val-C-C-3'NH2A esters are completely stable. Removal of the methoxy group of O-methylthreonine as in alpha-amino-butyric acid increases the rate of the hydrolytic reaction and once again alpha-Abu-tRNA Val-C-C-A and alpha-Abu-tRNA Val-C-C-3'dA are unstable under aminoacylating conditions and not isolable.
mesh_terms: D000604:Amino Acyl-tRNA Synthetases / Q000378:metabolism*; D001665:Binding Sites; D007533:Isoleucine-tRNA Ligase / Q000378:metabolism; D007700:Kinetics; D011485:Protein Binding; D012343:RNA, Transfer; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D013329:Structure-Activity Relationship; D013912:Threonine / Q000031:analogs & derivatives; D013914:Threonine-tRNA Ligase / Q000378:metabolism; D014633:Valine; D014637:Valine-tRNA Ligase / Q000378:metabolism
chemical_list: D013912:Threonine; D012343:RNA, Transfer; D000604:Amino Acyl-tRNA Synthetases; D013914:Threonine-tRNA Ligase; D007533:Isoleucine-tRNA Ligase; D014637:Valine-tRNA Ligase; D014633:Valine