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Mutant strains ofEscherichia coli K-12 have been isolated in which the synthesis of 3-deoxy-d -arabinoheptulosonic acid-7-phosphate (DAHP) synthetase (trp) is partially constitutive. The mutation causing derepression is closely linked toaroH [the structural gene for DAHP synthetase (trp)] and occurs in a locus designatedaroJ . ThearoJ mutation is not recessive in anaroJ + /aroJ − diploid strain, as the synthesis of DAHP synthetase (trp) is still derepressed in this strain. On the basis of its close linkage toaroH and its continued expression in anaroJ + /aroJ − diploid, it is postulated thataroJ is an operator locus controlling the expression of the structural genearoH . In support of this conclusion, the synthesis of anthranilate synthetase is still normally repressible inaroJ − strains, whereas, intrpR − strains, both DAHP synthetase (trp) and anthranilate synthetase are synthesized constitutively. The synthesis of DAHP synthetase (trp) remains repressible in an operator-constitutive mutant of the tryptophan operon. In twotrpS mutants which possess defective tryptophanyl transfer ribonucleic acid synthetase enzymes, neither DAHP synthetase (trp) nor anthranilate synthetase derepress under conditions in which the defective synthetase causes a decrease in growth rate. On the other hand, an effect of thetrpS mutant alleles on the level of anthranilate synthetase has been observed in strains which are derepressed for the synthesis of this enzyme, because of a mutation in the genetrpR . Possible explanations for this effect are presented.

journal of bacteriology

Repression of 3-Deoxy- <scp>d</scp> -Arabinoheptulosonic Acid-7-Phosphate Synthetase (trp) and Enzymes of the Tryptophan Pathway in <i>Escherichia coli</i> K-12

Repression of 3-Deoxy- d -Arabinoheptulosonic Acid-7-Phosphate Synthetase (trp) and Enzymes of the Tryptophan Pathway in Escherichia coli K-12