ISOLATION AND PROPERTIES OF MUTANTS OF ESCHERICHIA COLI WITH INCREASED PHOSPHORYLATION OF THIOMETHYL-BETA-GALACTOSIDE

Mutants of Escherichia coli were isolated which accumulated abnormally large amounts of radioactivity when cells were incubated in the presence of [14C]thiomethyl-β-galactoside ([14C]TMG). In addition to the normal amounts of free TMG, the mutant cells contained large quantities of phosphorylated TMG. Time-course studies showed that accumulation of free TMG precedes phosphorylation. The greater capacity of the intact mutant cells to phosphorylate TMG was confirmed with sonicated preparations. Evidence was obtained that the phosphorylation was catalyzed by a phosphoenolpyruvate-dependent phosphotransferase system. β-Galactoside transport negative (y-) mutants isolated from the hyper-phosphorylating mutants retained their increased capacity to phosphorylate TMG. While the natural substrate for this phosphorylation system is not yet clear, the system does not seem to be essential for the membrane transport of TMG. © 1969.