Glucose catabolite repression in Escherichia coli K12 mutants defective in methyl-alpha-d-glucoside transport.

1. Two spontaneous Escherichia coli K12 mutants resistant to glucose catabolite repression were isolated using minimal agar plates with methyl alpha-D-glucoside. Mutants grow well on glucose and mannitol. 2. Glucose does not inhibit the inducible enzyme synthesis in isolated mutants: mutant cell (in contrast to parent cells) produce high levels of beta-galactosidase and L-tryptophanase under the conditions of glucose catabolite repression. 3. The isolated mutants are negative in methyl-alpha-D-glucoside transport; glucose uptake is not severely damaged. But the mutants (named tgl, transport of glucose) retained the ability to phosphorylate methyl alpha-D-glucoside in vitro at the expense of phosphoenolpyruvate. 4. The tgl mutation is cotransduced with purB and pyrC markers, i.e. locates near 24 min of the E. coli chromosome map. 5. It is thought that E. coli cells possess two glucose transport systems. The first one is represented by the glucose-specific enzyme II of the phosphoenolpyruvate-dependent phosphotransferase system. The second glucose transport system (coded for tgl gene) functions as permease and possesses high affinity to methyl alpha-D-glucoside. The integrity of glucose permease determine the sensitivity of the cell to glucose catabolite repression.