Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:6.1.1.18 (glutaminyl-tRNA synthetase)
 231 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have isolated temperature resistant revertants from temperature sensitive E. coli strains containing either a thermolabile glutaminyl-tRNA synthetase or leucyl-tRNA synthetase. Among the revertants which still contained the thermolabile leucyl-tRNA synthetase we found two classes of regulatory mutants (leuX and leu Y) which have elevated levels of this enzyme. The leuX mutation specifies an operator-promoter region adjacent to the structural gene (leuS) for the enzyme. The leuY gene maps away from the leuS gene and codes for a protein. Using these mutants we demonstrated that the levels of leucyl-tRNA are related to the derepression of the leucine and isoleucine-valine operons. Among the revertants which still contained the thermolabile glutaminyl-tRNA synthetase were characterized three classes of mutants, glnT, glnU, and glnR. The glnT and glnU mutants contain elevated levels of tRNAgln, while the glnR mutant possesses elevated levels of glutaminyl-tRNA synthetase. The level of glutamine synthetase, the enzyme responsible for the formation of glutamine, is also derepressed in the glnT and glnR mutants.
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PMID:Regulation of biosynthesis of aminoacyl-transfer RNA synthetases and of transfer-RNA in Escherichia coli. 4 19

Thermus thermophilus possesses an aspartyl-tRNA synthetase (AspRS2) able to aspartylate efficiently tRNAAsp and tRNAAsn. Aspartate mischarged on tRNAAsn then is converted into asparagine by an omega amidase that differs structurally from all known asparagine synthetases. However, aspartate is not misincorporated into proteins because the binding capacity of aminoacylated tRNAAsn to elongation factor Tu is only conferred by conversion of aspartate into asparagine. T. thermophilus additionally contains a second aspartyl-tRNA synthetase (AspRS1) able to aspartylate tRNAAsp and an asparaginyl-tRNA synthetase able to charge tRNAAsn with free asparagine, although the organism does not contain a tRNA-independent asparagine synthetase. In contrast to the duplicated pathway of tRNA asparaginylation, tRNA glutaminylation occurs in the thermophile via the usual pathway by using glutaminyl-tRNA synthetase and free glutamine synthesized by glutamine synthetase that is unique. T. thermophilus is able to ensure tRNA aminoacylation by alternative routes involving either the direct pathway or by conversion of amino acid mischarged on tRNA. These findings shed light on the interrelation between the tRNA-dependent and tRNA-independent pathways of amino acid amidation and on the processes involved in fidelity of the aminoacylation systems.
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PMID:Thermus thermophilus: a link in evolution of the tRNA-dependent amino acid amidation pathways. 978