Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.6.1.1 (aspartate aminotransferase)
 21,665 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

4-Fluorophenylalanine-resistant mutants of Salmonella typhimurium were isolated in which tyrosine pathway enzymes were not repressed by l-tyrosine. The mutants produced elevated levels of 3-deoxy-d-arabinoheptulosonic acid 7-phosphate (DAHP) synthetase (tyr) and chorismate mutase T-prephenate dehydrogenase, and these enzymes as well as transaminase A were not repressed by high concentrations of tyrosine. Genetic analysis revealed that a mutation in a gene designated tyrR was responsible for the constitutivity of the tyrosine pathway enzymes in strains SG1, SG7, and SG9, and that tyrR was linked to pyrF. In strain SG1 a mutation had also occurred in aroF, the structural gene for DAHP synthetase (tyr), resulting in loss of sensitivity of this enzyme to end-product inhibition. There appeared to be no relationship between loss of feedback inhibition and loss of end-product repression, since derivative strains of SG1 that carried only the tyrR mutation behaved like the singly mutated tyrR strains, SG7 and SG9, in showing high constitutive levels of tyrosine-specific enzymes that were not repressed by tyrosine.
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PMID:tyrR, a regulatory gene of tyrosine biosynthesis in Salmonella typhimurium. 414 3

Mutants of Escherichia coli K-12 were isolated in which the synthesis of the following, normally repressible enzymes of aromatic biosynthesis was constitutive: 3-deoxy-d-arabinoheptulosonic acid 7-phosphate (DAHP) synthetases (phe and tyr), chorismate mutase T-prephenate dehydrogenase, and transaminase A. In the wild type, DAHP synthetase (phe) was multivalently repressed by phenylalanine plus tryptophan, whereas DAHP synthetase (tyr), chorismate mutase T-prephenate dehydrogenase, and transaminase A were repressed by tyrosine. DAHP synthetase (tyr) and chorismate mutase T-prephenate dehydrogenase were also repressed by phenylalanine in high concentration (10(-3)m). Besides the constitutive synthesis of DAHP synthetase (phe), the mutants had the same phenotype as strains mutated in the tyrosine regulatory gene tyrR. The mutations causing this phenotype were cotransducible with trpA, trpE, cysB, and pyrF and mapped in the same region as tyrR at approximately 26 min on the chromosome. It is concluded that these mutations may be alleles of the tyrR gene and that synthesis of the enzymes listed above is controlled by this gene. Chorismate mutase P and prephenate dehydratase activities which are carried on a single protein were repressed by phenylalanine alone and were not controlled by tyrR. Formation of this protein is presumed to be controlled by a separate, unknown regulator gene. The heat-stable phenylalanine transaminase and two enzymes of the common aromatic pathway, 5-dehydroquinate synthetase and 5-dehydroquinase, were not repressible under the conditions studied and were not affected by tyrR. DAHP synthetase (trp) and tryptophan synthetase were repressed by tryptophan and have previously been shown to be under the control of the trpR regulatory gene. These enzymes also were unaffected by tyrR.
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PMID:Repression of aromatic amino acid biosynthesis in Escherichia coli K-12. 439 41