Induction of the ara operon of Escherichia coli B-r

The inducer specificity and kinetics of induction of the ara operon were examined in Escherichia coli B/r. A difference in the kinetics of induction was found between our B/r strains and the K-12 strain previously described by Schleif. The roles of active transport and metabolism of inducer, and of cell density, in induction were studied. d-Fucose and beta-methyl-l-arabinoside were competitive inhibitors of induction. No inducer of the wild-type strain other than l-arabinose was found. However, a procedure for selecting mutants with altered inducer affinity or specificity was developed. The properties of one such mutant (inducible by d-fucose) are described.