The first enzyme of the gal operon in inducible and operator-constitutive strains of Escherichia coli. A comparison of the porperties and amino-terminal sequences of UDP galactose 4-epimerase.

1. UDPgalactose 4-epimerase, the product of the first structural gene of the gal operon in Escherichia coli K-12, has been purified from strain HfrH and from its gal operator-constitutive mutant, HfrH 81-2. 2. The two enzymes are purified by the same procedure, behaving identically throughout. They are identical in sedimentation coefficient, sioelectric point, electrophoretic mobility at pH 8.8 and amino-terminal sequence for the first 30 residues. 3. Slight but reporducible differences were observed between the amino acid compositions and peptide maps of the two proteins. These differences may indicate real differences in the primary sequences of the proteins, but if so they are unlikely to be due to the operator-constitutive mutation because of the identy of the sequences for the first 30 residues. 4. No evidence was found to indicate that the gal operator might overlap with the first structural gene.