Affiliation:
1. School of Microbiology, University of Melbourne, Parkville, Victoria, Australia
Abstract
Mutant strains of
Escherichia 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 to
aroH
[the structural gene for DAHP synthetase (trp)] and occurs in a locus designated
aroJ
. The
aroJ
mutation is not recessive in an
aroJ
+
/
aroJ
−
diploid strain, as the synthesis of DAHP synthetase (trp) is still derepressed in this strain. On the basis of its close linkage to
aroH
and its continued expression in an
aroJ
+
/
aroJ
−
diploid, it is postulated that
aroJ
is an operator locus controlling the expression of the structural gene
aroH
. In support of this conclusion, the synthesis of anthranilate synthetase is still normally repressible in
aroJ
−
strains, whereas, in
trpR
−
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 two
trpS
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 the
trpS
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 gene
trpR
. Possible explanations for this effect are presented.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
22 articles.
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