Soffer, Richard L. (Stanford University, Palo Alto, Calif.). Enzymatic expression of genetic units of function concerned with galactose metabolism in Escherichia coli. J. Bacteriol. 82:471-478. 1961.-A series of genetically characterized galactose-negative mutants of Escherichia coli strain K12 were studied with respect to the enzymes of the Leloir pathway for utilization of this sugar. The functions pertaining to the three genetically defined cistrons were found to relate, respectively, to the expression of galactokinase, galactose 1-phosphate uridyl transferase, and uridine diphosphate galactose 4-epimerase. Mutants defective in the latter enzyme represent a new biochemical class in this strain of E. coli. Most of the mutants defective in galactokinase were found to exhibit significantly elevated levels of galactose 1-phosphate uridyl transferase as compared with the wild type when grown under conditions of induction. A suppressed transferase-deficient mutant was found to have regained this enzymatic activity.