The Regulation and Properties of the Galactose Transport System in Escherichia coli K12

This study of galactose-induced transport in Escherichia coli K12 showed that in most strains two transport systems having the properties of galactose permease and galactoside permease are responsible for the observed transport. Several strains contain only the transport system but still grow normally on galactose. The regulation of this system was shown to be very similar to that of the operon. That is, it is induced by galactose, shows only a slight repression by glucose, and is under the control of the regulator gene. The only differences between the regulations of the transport system and that of the enzymes are the level of induction (4-fold for the transport system versus 15-fold for the enzymes) and the fact that the transport system is not under the control of the operator locus. The β-methyl galactoside transport system is not regulated by either regulatory gene in agreement with the work of Lengeler et al. (Lengeler, J., Hermann, K.O., Unsold, H.J. & Boos, W. (1971) Eur. J. Biochem. 19, 457–470). Galactose-binding protein is not essential for the activity of the transport system as there is no correspondence between the level of the two. In fact, the transport system is present at near normal levels under conditions where there is no measurable binding protein activity. Although the and β-methyl galactoside transport systems have different genetic loci and are controlled by different regulatory systems, they do not function independently when they are both present in the same cell. Rather, they interact in a complex way that results in the rate of transport by the β-methyl galactoside system being reduced at high concentrations and the Km of transport by the system being reduced 3-fold.