Escherichia coli mutants deficient in the aspartate and aromatic amino acid aminotransferases

J Bacteriol. 1977 Apr;130(1):429-40. doi: 10.1128/jb.130.1.429-440.1977.


Two new mutations are described which, together, eliminate essentially all the aminotransferase activity required for de novo biosynthesis of tyrosine, phenylalanine, and aspartic acid in a K-12 strain of Escherichia coli. One mutation, designated tyrB, lies at about 80 min on the E. coli map and inactivates the "tyrosine-repressible" tyrosine/phenylalanine aminotransferase. The second mutation, aspC, maps at about 20 min and inactivates a nonrespressible aspartate aminotransferase that also has activity on the aromatic amino acids. In ilvE- strains, which lack the branched-chain amino acid aminotransferase, the presence of either the tyrosine-repressible aminotransferase or the aspartate aminotransferase is sufficient for growth in the absence of exogenous tyrosine, phenylalanine, or aspartate; the tyrosine-repressible enzyme is also active in leucine biosynthesis. The ilvE gene product alone can reverse a phenylalanine requirement. Biochemical studies on extracts of strains carrying combinations of these aminotransferase mutations confirm the existence of two distinct enzymes with overlapping specificities for the alpha-keto acid analogues of tyrosine, phenylalanine, and aspartate. These enzymes can be distinguished by electrophoretic mobilities, by kinetic parameters using various substrates, and by a difference in tyrosine repressibility. In extracts of an ilvE- tyrB- aspC- triple mutant, no aminotransferase activity for the alpha-keto acids of tyrosine, phenylalanine, or aspartate could be detected.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Aspartate Aminotransferases / metabolism*
  • Aspartic Acid / biosynthesis
  • Chromosome Mapping
  • Chromosomes, Bacterial
  • Coliphages
  • Escherichia coli / enzymology*
  • Genes*
  • Leucine / biosynthesis
  • Mutation
  • Phenylalanine / biosynthesis
  • Transaminases / metabolism*
  • Transduction, Genetic
  • Tyrosine / biosynthesis
  • Tyrosine Transaminase / metabolism*


  • Aspartic Acid
  • Tyrosine
  • Phenylalanine
  • Transaminases
  • Aspartate Aminotransferases
  • Tyrosine Transaminase
  • Leucine