The regulation of the beta-methylgalactoside transport system and of the galactose binding protein of Escherichia coli K12.

Abstract

In the present publication the synthesis of the galactose binding protein and the β-methyl-galactoside transport system in Escherichia coli K12 has been shown to be coregulated. With the use of mutants of different regulatory behavior with respect to the galactose operon and the phosphoenolpyruvate-dependent phosphotransferase system, the following information about the regulation of the simultaneous synthesis of the galactose binding protein and the β-methyl-galactoside transport system was obtained. 1 Fucose acts as inducer for both the galactose binding protein and the transport system. 2 GalK mutants, endogenously induced with respect to the galactose operon, also show endogenous induction of the transport system. 3 The induction by fucose as well as endogenous induction is inhibited by 5 mM methyl-1-thio-β-D-galactopyranoside. 4 GalR+, galR and galRs mutants can show full inducibility, excluding the function of galR in the regulation of the β-methylgalactoside transport system. 5 Deletions of the entire galactose operon exhibit high yet inducible transport activities excluding the existence of a regulator gene near or in the galactose operon. 6 The existence of a regulator gene mglR which is different from galR, melR lacI, araC or pts could be demonstrated. The mutation mglR was found to be located between the origin of two Hfr strains, AB313 and KL16, i.e. between 56 and 74 min on the linkage map of E. coli. 7 Mutants defective in enzyme I activity of the phosphoenolpyruvate-dependent phosphotransferase system exhibit unimpaired β-methylgalactoside transport activity excluding any function of the β-methylgalactoside permease as a specific enzyme II of the phosphotransferase system.