Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:6.1.1.4 (leucyl-tRNA synthetase)
 297 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Altered leucyl-tRNA synthetase from a mammalian cell culture temperature-sensitive mutant, tsHl, was compared with enzyme from normal wild type Chinese hamster ovary cells. The mutant enzyme had a Km for leucine four times larger than that of wild type and enzyme levels 3-10% that of wild type. The presence of tRNA was necessary during in vitro heating of the mutant enzyme to allow expression of thermolability while the presence of tRNA protected wild type enzyme against thermal inactivation. The tsHl enzyme was stable when heated alone or in the presence of tRNA, leucine, and ATP simultaneously. The mutant's enzymes aminoacylated tRNALeu, tRNAVal, and tRNAIle with fidelity in vitro as determined by cochromatography of the amino-acyl-tRNA isoacceptors on RPC-5 reversed phase chromatography. The mutant failed to show any defect other than the direct formation of leucyl tRNALeu by leucyl-tRNA synthetase.
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PMID:Altered leucyl-transfer RNA synthetase from a mammalian cell culture mutant. 1 33

The extent of esterification of [14C] leucine into Escherichia coli B tRNALeu apparently depends on the concentration of leucyl-tRNA synthetase. The effect is more pronounced at pH 9.0 than at pH 7.4. When reciprocals of leucyl-tRNA concentration at plateau [aa-tRNA]-1 are plotted against reciprocals of initial velocities vo-1 of aminoacylations a straight line is obtained with a slope equal to the rate constant of non-enzymatic deacylation of leucyl-tRNA. Factors which change the stability of leucyl-tRNA, e.g. pH and temperature, also change the shape of the function [aa-tRNA]-1 vs. vo-1. The data are consistent with the idea that the rate constant of spontaneous deacylation of aminoacyl-tRNA is the factor which accounts for the dependence of the level of aminoacylation on initial velocity of aminoacylation.
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PMID:Incomplete aminoacylation of tRNALeu catalyzed in vitro by leucyl-tRNA synthetase from Escherichia coli B. 2 6

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

At concentrations of 1-1.6 mug/ml, 5,8-dioxo-6-amino-7-chloroquinoline causes auxotrophy for leucine in Escherichia coli MRE 600. With increasing concentrations of this quinone additional amino acids are required for growth. The amount of leucine in the pool of free amino acids is not decreased after treatment of E. coli with the quinone. Transfer RNALeu, however, is charged with leucine less than 10% in quinone-treated cells of E. coli, whereas in control cells the degree of aminoacylation is about 85%. From these data we conclude that the quinone causes auxotrophy for leucine by interacting with the charging process of tRNALeu. Quinone was found to inhibit leucyl-tRNA synthetase activity in purified extracts of E. coli with E. coli tRNA as substrate.
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PMID:Inhibition of leucyl-tRNA synthetase in Escherichia coli by the cytostatic 5,8-dioxo-6-amino-7-chloroquinoline. 9 89

Genetic analysis of an electrophoretic variant of the mitochondrial leucyl-tRNA synthetase [L-leucine:tRNALeu ligase (AMP-forming), EC 6.1.1.4] indicates that it is either an allele of or linked closely to leu-5ts, a mutant that is known to produce a cytoplasmic leucyl-tRNA synthetase with an altered affinity for leucine as well as being deficient in the production of the mitochondrial enzyme. Immunological analysis indicates that the two synthetases have little, if any, structural homology. The pattern of synthesis of the enzymes in leu-5ts revertants, the reciprocal relationship of the production of the two enzymes in response to a negative regulatory element, presumably of mitochondrial origin, as well as the lack of detectable structural homology, led to the proposal that the phenotype of leu-5ts results from a mutational alteration in the structural gene for the cytoplasmic enzyme in a region involved in the initiation of transcription of the adjacent gene for the mitochondrial enzyme.
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PMID:Proposed involvement of an internal promoter in regulation and synthesis of mitochondrial and cytoplasmic leucyl-tRNA synthetases of Neurospora. 13 9

The partition behavior of isoleucyl-tRNA synthetase, leucyl-tRNA synthetase and tRNA in aqueous two-phase systems composed of the polymers poly(ethyleneglycol) and dextran was investigated. From the results of this investigation a two-phase system could be derived which can be employed for the study of the interactions between synthetases and their cognate tRNAs by equilibrium partition. These measurements show that in each case one molecule of cognate tRNA is bound per molecule of enzyme. The binding constants were in the range 1-5micronM-1. It could be demonstrated that equilibrium partition is a useful method for the study of interactions between macromolecules.
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PMID:Studies of the interaction between aminoacyl-tRNA synthetase and transfer ribonucleic acid by equilibrium partition. 32 6

Valyl-, isoleucyl-, and leucyl-tRNA synthetase activities were examined in an Escherichia coli K-12 strain that possessed a deletion of three genes of the ilv gene cluster, ilvD, A, and C, and in a strain with the same deletion that also carried the lambdadilvCB bacteriophage. It was observed that the branched-chain tRNA synthetase activities of both strains were considerably less than those of the normal strain during growth in unrestricted medium. Furthermore, during an isoleucine limitation, there was a further reduction in isoleucyl-tRNA synthetase activity and an absence of the isoleucine-mediated derepression of valyl-tRNA synthetase formation in both of these mutants, as compared with the normal strain. In addition, it was observed that these branched-chain synthetase activities were reduced in steady-state cultures of several ilvA point mutants. However, upon the introduction of the ilv operon to these ilvA mutants by use of lambda bacteriophage, there was a specific increase in the branched-chain synthetase activities to levels comparable to those of the normal strain. These results support our previous findings that the stability and repression control of synthesis of these synthetases require some product(s) missing in the ilvDAC deletion strain and strongly suggest this component is some form of the ilvA gene product, threonine deaminase.
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PMID:Synthesis and activities of branched-chain aminoacyl-tRNA synthetases in threonine deaminase mutants of Escherichia coli. 34 89

Leucyl-tRNA synthetase from Escherichia coli is rapidly inactivated by 6-amino-7-chloro-5,8-dioxoquinoline (quinone), a model substance for cytostatic quinones. Loss of activity follows pseudo-first order kinetics. The quinone masks essential--SH groups that are reactive with N-ethylmaleimide. Specific protection of the enzyme by leucine provides evidence for active site-directed modification. Half-maximal protection is found at a concentration of 150 micron which is identical with the dissociation constant of the enzyme.substrate complex. The competitive inhibitor leucinol also protects the enzyme from inactivation by the quinone. MgATP enhances the protective effect of leucinol about 250-fold, thus substantiating recently published findings on synergistic coupling of ligands to aminoacyl-tRNA synthetases. The results support the assumption that the bacteriostatic quinone directly interferes with leucyl-tRNA synthetase in growing cells. Active-site-directed inhibition of the enzyme could adequately explain the phenotypically observed auxotrophy for leucine of quinone-treated E. coli.
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PMID:The molecular basis of leucine auxotrophy of quinone-treated Escherichia coli. Active site-directed modification of leucyl-tRNA synthetase by 6-amino-7-chloro-5,8-dioxoquinoline. 36 53

Spontaneous revertants of a temperature-sensitive Escherichia coli strain harboring a thermolabile leucyl-tRNA synthetase and seryl-tRNA synthetase were selected for growth at 40 degrees C. Among these, strains were found with increased levels of both thermolabile synthetases. Two distinct genetic loci were found responsible for enzyme overproduction. leuR, located near xyl, causes elevated levels of leucyl-tRNA synthetase; while serR, located near leu, causes elevated levels of seryl-tRNA synthetase.
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PMID:Regulation of the biosynthesis of aminoacyl-tRNA synthetases and of tRNA in Escherichia coli. IV. Mutants with increased levels of leucyl- or seryl-tRNA synthetase. 37 9

A procedure for the large-scale isolation of leucyl-tRNA synthetase from E. cole MRE 600 is described: The enzyme was purified about 320-fold to homogeneity by precipitation with cetyl-trimethyl-ammonium bromide, two consecutive chromatographies on DEAE-cellulose and three on hydroxyapatite with an over-all yield of 4%. The molecular weight of leucyl-tRNA synthetase from E. coli MRE 600 was found to be 99 000 daltons. Bindings studies by ultracentrifugation and equilibrium partition showed that the enzyme binds leucine, leucyl-adenylate and tRNA Leu, each in a 1 : 1 stoichiometry. For ATP only a very weak binding to the enzyme could be observed, which did not allow the evaluation of the complex stoichiometry. The presence of ATP was not required for the binding of leucine or tRNA to leucyl-tRNA synthetase from E. coli MRE 600.
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PMID:Isolation and binding properties of leucyl-tRNA synthetase from Escherichia coli MRE 600. 37 93


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