Cryptic Operon for β-Glucoside Metabolism in ESCHERICHIA COLI K12: Genetic Evidence for a Regulatory Protein

摘要

Escherichia coli K12 does not metabolize β-glucosides such as arbutin and salicin because of lack of expression of the bglBSRC operon, which contains structural genes for transport (bglC) and hydrolysis (bglB) of phospho-β-glucosides. Mutants carrying lesions in the cis-acting regulatory site bglR metabolize β-glucosides as a consequence of expression of this cryptic operon (Prasad and Schaefler 1974). We isolated mutations promoting β-glucoside metabolism that were unlinked to bglR; some of these mutations were shown to be amber. All of them were mapped at 27 min on the E. coli K12 linkage map and appeared to define a single gene, for which we propose the designation bglY. Utilization of β-glucosides in bglY mutants appeared to be a consequence of expression of the bglBSRC operon, since bglB bglR and bglB bglY double mutants had the same phenotype. All bglY mutations analyzed were recessive to the wild-type bglY⁺ allele. Phospho-β-glucosidase B and β-glucoside transport activities are inducible in bglY mutants, as they are in bglR mutants. Metabolism of β-glucosides in both bglR and bglY mutants required cyclic AMP. We propose that bglY encodes a protein acting as a repressor of the bglBSRC operon, active in both the presence and absence of β-glucosides, whose recognition site would be within the bglR locus.