| Abstract: | Escherichia coli wild-type cells form constitutively the enzyme phospho-β-glucosidase A, which has a high affinity for phosphorylated aromatic β-glucosides and a low affinity for phosphorylated β-methyl-glucoside. Phospho-β-glucosidase B and β-glucoside permease I are formed in aromatic β-glucoside-fermenting mutants. Mutants lacking phospho-β-glucosidases A and B have been isolated. These mutants showed a reduced rate of inducibility of the β-glucoside permease I. The restoration of phospho-β-glucosidase A or B activity resulted in an increased rate of induction of the β-glucoside permease I. The presence of the phospho-β-glucosidases was not required for the constitutive biosynthesis of the β-glucoside permease. Mutants selected for growth on β-methyl-glucoside as carbon source showed an increased level of constitutive phospho-β-glucosidase A activity. Gene bglD, the structural gene for phospho-β-glucosidase A, was mapped between the pyrE locus and the cluster bgl loci, whereas bglE, the regulatory site determining the hyperproduction of phospho-β-glucosidase A, was mapped between the bgl and ilv clusters. The bglE locus appears to have a regulatory effect on the expression of the bglD gene. |
