Mutations in Escherichia coli that affect uridine diphosphate glucose pyrophosphorylase activity and galactose fermentation

Abstract

The metabolism of galactose was studied in two galactose-non-fermenting mutants which were isolated from Escherichia coli strain K12 and classified genetically as Group E by Drs. J. and E. M. Lederberg. One of them, W4597, was found to have a single defect in UDPG pyrophosphorylase (UTP: α-d-glucose-1-phosphate uridylyltranserase, EC 2.7.7.9) and to be normal in galactokinase (ATP: d-galactose 1-phosphotransferase, EC 2.7.1.6), Gal-1-P uridyl transferase (UDP glucose: α-d-galactose-1-phosphate uridylyl transferase, EC 2.7.7.12), UDP galactose 4-epimerase (UDP glucose 4-epimerase, EC 5.1.3.2), phosphoglucomutase (d-glucose-1,6-diphosphate: d-glucose-1-phosphate phosphotransferase, EC 2.7.5.1), and also in galactose permease. Non-fermentation of galactose in this strain was, therefore, ascribed to the defect of UDPG pyrophosphorylase. The other strain, W3142, was shown to have a secondary defect in galactokinase in addition to a defect in UDPG pyrophosphorylase. When grown in the presence of galactose, W4597 accumulated intracellularly a large amount of Gal-1-P.The intracellular levels of UDPG and uridine diphosphate galactose were shown to be much lower in both of these strains than in wild-type strains, irrespective of the presence or absence of galactose in the growth media. The sugars of their cell walls were composed only of an aldoheptose, hexosamines and a smaller amount of glucose; any traces of galactose, which is present in wild type cell walls, were not detected in their cell walls.