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Query: EC:6.1.1.10 (methionyl-tRNA synthetase)
 387 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Five aminoacyl-tRNA synthetases found in the high molecular weight core complex were phosphorylated in rabbit reticulocytes following labeling with 32P. The synthetases were isolated by affinity chromatography on tRNA-Sepharose followed by immunoprecipitation. The five synthetases phosphorylated were the glutamyl-, glutaminyl-, lysyl-, and aspartyl-tRNA synthetases and, to a lesser extent, the methionyl-tRNA synthetase. In addition, a 37,000-dalton protein, associated with the synthetase complex and tentatively identified as casein kinase I, was also phosphorylated in intact cells. Phosphoamino acid analysis of the proteins indicated all of the phosphate was on seryl residues. Incubation of reticulocytes with 32P in the presence of 8-bromo-cAMP and 3-isobutyl-1-methylxanthine resulted in a 6-fold increase in phosphorylation of the glutaminyl-tRNA synthetase and a 2-fold increase in phosphorylation of the aspartyl-tRNA synthetase. When the high molecular weight core complex was isolated by gel filtration/affinity chromatography, the profile of phosphorylation was similar to that observed by immunoprecipitation with a 9- and 3-fold stimulation of the glutaminyl- and aspartyl tRNA-synthetase, respectively. From this data it was concluded that the increased phosphorylation of the glutaminyl- and aspartyl-tRNA synthetases obtained with 8-bromo-cAMP did not appear to be involved in dissociation of the high molecular weight core complex.
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PMID:Regulation of phosphorylation of aminoacyl-tRNA synthetases in the high molecular weight core complex in reticulocytes. 243 10

A derivative of Escherichia coli tRNAfMet containing an altered anticodon sequence, CUA, has been enzymatically synthesized in vitro. The variant tRNA was prepared by excision of the normal anticodon, CAU, in a limited digestion of intact tRNAfMet with RNase A, followed by insertion of the CUA sequence into the anticodon loop with T4 RNA ligase and polynucleotide kinase. The altered methionine tRNA showed a large enhancement in the rate of aminoacylation by glutaminyl-tRNA synthetase and a large decrease in the rate of aminoacylation by methionyl-tRNA synthetase. Measurement of kinetic parameters for the charging reaction by the cognate and noncognate enzymes revealed that the modified tRNA is a better acceptor for glutamine than for methionine. The rate of mischarging is similar to that previously reported for a tryptophan amber suppressor tRNA containing the anticodon CUA, su+7 tRNATrp, which is aminoacylated with glutamine both in vivo and in vitro [Yaniv, M., Folk, W. R., Berg, P., & Soll, L. (1974) J. Mol. Biol. 86, 245-260; Yarus, M., Knowlton, R. E., & Soll, L. (1977) in Nucleic Acid-Protein Recognition (Vogel, H., Ed.) pp 391-408, Academic Press, New York]. The present results provide additional evidence that the specificity of aminoacylation by glutaminyl-tRNA synthetase is sensitive to small changes in the nucleotide sequence of noncognate tRNAs and that uridine in the middle position of the anticodon is involved in the recognition of tRNA substrates by this enzyme.
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PMID:In vitro conversion of a methionine to a glutamine-acceptor tRNA. 391 Jan 1

We report that aminoacylation of minimal RNA helical substrates is enhanced by mismatched or unpaired nucleotides at the first position in the helix. Previously, we demonstrated that the class I methionyl-tRNA synthetase aminoacylates RNA microhelices based on the acceptor stem of initiator and elongator tRNAs with greatly reduced efficiency relative to full-length tRNA substrates. The cocrystal structure of the class I glutaminyl-tRNA synthetase with tRNAGln revealed an uncoupling of the first (1.72) base pair of tRNAGln, and tRNAMet was proposed by others to have a similar base-pair uncoupling when bound to methionyl-tRNA synthetase. Because the anticodon is important for efficient charging of methionine tRNA, we thought that 1.72 distortion is probably effected by the synthetase-anticodon interaction. Small RNA substrates (minihelices, microhelices, and duplexes) are devoid of the anticodon triplet and may, therefore, be inefficiently aminoacylated because of a lack of anticodon-triggered acceptor stem distortion. To test this hypothesis, we constructed microhelices that vary in their ability to form a 1.72 base pair. The results of kinetic assays show that microhelix aminoacylation is activated by destabilization of this terminal base pair. The largest effect is seen when one of the two nucleotides of the pair is completely deleted. Activation of aminoacylation is also seen with the analogous deletion in a minihelix substrate for the closely related isoleucine enzyme. Thus, for at least the methionine and isoleucine systems, a built-in helix destabilization compensates in part for the lack of presumptive anticodon-induced acceptor stem distortion.
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PMID:Activation of microhelix charging by localized helix destabilization. 977 Apr 66

The mode of recognition of tRNAs by aminoacyl-tRNA synthetases and translation factors is largely unknown in archaebacteria. To study this process, we have cloned the wild type initiator tRNA gene from the moderate halophilic archaebacterium Haloferax volcanii and mutants derived from it into a plasmid capable of expressing the tRNA in these cells. Analysis of tRNAs in vivo show that the initiator tRNA is aminoacylated but is not formylated in H. volcanii. This result provides direct support for the notion that protein synthesis in archaebacteria is initiated with methionine and not with formylmethionine. We have analyzed the effect of two different mutations (CAU-->CUA and CAU-->GAC) in the anticodon sequence of the initiator tRNA on its recognition by the aminoacyl-tRNA synthetases in vivo. The CAU-->CUA mutant was not aminoacylated to any significant extent in vivo, suggesting the importance of the anticodon in aminoacylation of tRNA by methionyl-tRNA synthetase. This mutant initiator tRNA can, however, be aminoacylated in vitro by the Escherichia coli glutaminyl-tRNA synthetase, suggesting that the lack of aminoacylation is due to the absence in H. volcanii of a synthetase, which recognizes the mutant tRNA. Archaebacteria lack glutaminyl-tRNA synthetase and utilize a two-step pathway involving glutamyl-tRNA synthetase and glutamine amidotransferase to generate glutaminyl-tRNA. The lack of aminoacylation of the mutant tRNA indicates that this mutant tRNA is not a substrate for the H. volcanii glutamyl-tRNA synthetase. The CAU-->GAC anticodon mutant is most likely aminoacylated with valine in vivo. Thus, the anticodon plays an important role in the recognition of tRNA by at least two of the halobacterial aminoacyl-tRNA synthetases.
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PMID:Importance of the anticodon sequence in the aminoacylation of tRNAs by methionyl-tRNA synthetase and by valyl-tRNA synthetase in an Archaebacterium. 1105 96

The catalytic domains of class I aminoacyl-tRNA synthetases are built around a conserved Rossmann nucleotide binding fold, with additional polypeptide domains responsible for tRNA binding or hydrolytic editing of misacylated substrates. Structural comparisons identified a conserved motif bridging the catalytic and anticodon binding domains of class Ia and Ib enzymes. This stem contact fold (SCF) has been proposed to globally orient each enzyme's cognate tRNA by interacting with the inner corner of the L-shaped tRNA. Despite the structural similarity of the SCF among class Ia/Ib enzymes, the sequence conservation is low. We replaced amino acids of the MetRS SCF with portions of the structurally similar glutaminyl-tRNA synthetase (GlnRS) motif or with alanine residues. Chimeric variants retained significant tRNA methionylation activity, indicating that structural integrity of the helix-turn-strand-helix motif contributes more to tRNA aminoacylation than does amino acid identity. In contrast, chimeras were significantly reduced in methionyl adenylate synthesis, suggesting a role for the SCF in formation of a structured active site domain. A highly conserved aspartic acid within the MetRS SCF is proposed to make an electrostatic interaction with an active site lysine; these residues were replaced with alanines or conservative substitutions. Both methionyl adenylate formation and methionine transfer were impaired, and activity was not significantly recovered by making the compensatory double substitution.
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PMID:Role for a conserved structural motif in assembly of a class I aminoacyl-tRNA synthetase active site. 2117 97