Phenylalanine and Tyrosine Biosynthesis in Escherichia coli K-12: Mutants Derepressed for 3-Deoxy- d -Arabinoheptulosonic Acid 7-Phosphate Synthetase (phe), 3-Deoxy- d -Arabinoheptulosonic Acid 7-Phosphate Synthetase (tyr), Chorismate Mutase T-Prephenate Dehydrogenase, and Transaminase A

Abstract

Mutant strains of Escherichia coli have been isolated in which the synthesis of 3deoxy-D-arabinoheptulosonic acid 7-phosphate (DAHP) synthetase (phe) is derepressed, in addition to those enzymes of tyrosine biosynthesis previously shown to be controlled by the gene tyrR. The major enzyme of the terminal pathway of phenylalanine biosynthesis chorismate mutase-prephenate dehydratase is not derepressed in these strains. Genetic analysis of the mutants shows that the mutation or mutations causing derepression map close to previously reported tyrR mutations. A study of one of the mutations has shown it to be recessive to the wild-type allele in a diploid strain. It is proposed that the tyrR gene product is involved in the regulation of the synthesis of DAHP synthetase (phe) as well as the synthesis of DAHP synthetase (tyr), chorismate mutase-prephenate dehydrogenase, and transaminase A.The first reaction of aromatic biosynthesis, the condensation of erythrose-4-phosphate and phosphoenolpyruvate to form 3-deoxy-D-arabinoheptulosonic acid 7-phosphate (DAHP) is carried out in Escherichia coli by three isoenzymes, the synthesis and activity of each of these isoenzymes being controlled by tyrosine, phenylalanine, and tryptophan, respectively (4, 10, 17). These amino acids also control the synthesis of one or more enzymes in each of the terminal pathways from chorismic acid to tyrosine, phenylalanine, and tryptophan (10). In the case of tyrosine biosynthesis, the structural genes for DAHP synthetase (tyr) and chorismate mutaseprephenate dehydrogenase (a key enzyme in the tyrosine pathway) form a single operon, the expression of which is controlled by a regulator gene tyrR (Mattern and Pittard, in press). In tryptophan biosynthesis, the structural gene for DAHP synthetase (trp) is separated from the structural genes of the trp operon; however, all three are subject to control by the regulator gene trpR (5, 14; Camakaris and Pittard, in press).The genes for DAHP synthetase (phe) and chorismate mutase-prephenate dehydratase are also separated from each other on the chromosome; although operator mutants controlling the expression of the gene for chorismate mutase-prephenate dehydratase have been described (Im and Pittard, in press), there have as yet been no reports of mutations affecting the synthesis of DAHP synthetase (phe). It is the purpose of this paper to describe the isolation and characterization of mutants derepressed for the synthesis of DAHP synthetase (phe). Although the method that was used to isolate these mutants was expected to select for strains derepressed for both chorismate mutase-prephenate dehydratase and DAHP synthetase (phe), chorismate mutaseprephenate dehydratase is not derepressed in these mutants. However, the observation that the tyrosine biosynthetic enzymes are also derepressed in these mutants suggests the possibility of some relationship in the control of the two pathways.In an accompanying paper (4a), Brown and So-400 on July 15, 2020 by guest

Aromatic amino acid biosynthesis: regulation of shikimate kinase in Escherichia coli K-12

“…Effect of mutations in the regulator genes trpR and tyrR on the synthesis of shikimate kinase. Both tryptophan and tyrosine, in concert with the product of the regulator genes trpR and tyrR, respectively, are involved in the repression of other enzymes of aromatic biosynthesis in E. coli (7,17,21,28,31,32,34). To test whether the product of either the trpR or tyrR gene is also involved in the repression of shikimate kinase, enzyme levels were measured in mutant strains in which one or other of the regulator gene products was nonfunctional.…”

“…Assay of chorismate mutase. The method described by Im et al (17) was used to assay chorismate mutase.…”

Regulation of aromatic amino acid transport systems in Escherichia coli K-12

“…)phan in phenylal-Effect of a tyrR mutation on transport JC411, the strain regulation. The tyrR gene has been shown to ived, did show en-code for an aporepressor that is involved in the tophan (data not control of the expression of at least four differhe increased activent genetic loci concerned with aromatic bioinvolves the previ-synthesis (8,10,13,24; Ely and Pittard, Proc. an-specific system.…”

tyrR, A Regulatory Gene of Tyrosine Biosynthesis in Salmonella typhimurium

“…Derepressed levels of this enzyme in fluorophenylalanineresistant transductants from either donor strain SG42 or SG32 confirmed that tyrR460 had been co-transduced with pyrF. In E. coli K-12, Im et al (14) found by transduction that tyrR showed about 4% linkage to trp and 13% linkage to pyrF. Brown and Somerville (3) found a higher frequency of linkage with their tyrR mutants.…”

“…Linkage of tyrR has been shown to both trp and pyrF in E. coli (3,14), whereas linkage could be established only to pyrF in Salmonella. However, the genome of bacteriophage P1 used in E. coli is larger than that of phage P22, and linkage may be obtained with genes that are not linked in Salmonella.…”