Proteins of the Lactose System

Addition of lactose or certain other galactosides to a growing culture of wild-type Escherichia coli results in the coordinate induction of 3 components: (1) β-galactosidase, the hydrolytic enzyme allowing utilization of lactose, (2) galactoside-permease which functions in the transport of lactose into the cell, and (3) thiogalactoside transacetylase, whose physiological role in the cell is not clear (Jacob and Monod 1961a, b). The latter enzyme, discovered a few years ago (Zabin, Kepes, and Monod, 1959, 1962), catalyses the transfer of an acetyl group from acetyl coenzyme A to a thiogalactoside acceptor as shown in Fig. 1.