Aspects of galactose and glucose transport in Escherichia coli.

1. Strains of E. co1i have been characterised which are galactose-positive despite their failure to express, any of the active transport systems for galactose during growth on this sugar. The growth of such strains on galactose occurs at rates that are a function of the galactose concentration of the medium: half-maximal growth rates require more than 2mM galactose to be present. The introduction of a mutation in the glucose phosphotransferase Enzyme II specified by the gene umg severely impairs the ability of these strains to grow on galactose; it has been established by a variety of means that this Enzyme II, or a component of it, provides the means of galactose entry into these organisms. However, the uptake of galactose does not require phosphotransferase activity, but occurs by facilitated diffusion on this carrier. The implications of this finding on the current understanding of tine mechanism of glucose uptake by the phosphotransferase system are discussed. 2. Although the Umg-system provides the major route of glucose uptake in many strains of E. co1i, this is not true for all strains. Evidence is presented that suggests the existence of a fourth Enzyme II for glucose, in addition to those specified by the genes umg, ptsX and bgl. 3. The galactose permease specified by the gene galP can transport glucose in addition to galactose. A screening procedure for distinguishing GalP+ from GalP- strains is described which makes use of this property and which has been used to locate the galP lesion close to minute 55 on the E. coli chromosome, between the genetic markers fda and lysA.