Lac operon The operon that controls the synthesis of acetylase, permease, and beta galactosidase, 3 enzymes involved in the metabolism of lactose in Escherichia coli. The Lac operon is a cluster of structural genes specifying the above enzymes. These genes are controlled by the co-ordinated action of cis-dominant promoter and operator regions, the activity of which is in turn determined by a repressor molecule that is specified by a separate regulator gene. Most of the detailed discovery of this system was worked out by François Jacob and Jacques Monod during the late 1950s and early 1960s; the Lac operon DNA was isolated in pure form in 1969.

lac operon The operon that regulates lactose metabolism in the bacterium Escherichia coli. Its form was first postulated in 1961 by François Jacob (1920– ) and Jacques Monod (1910–76) to explain control of β-galactosidase synthesis, and it is used as a model for the structure of all other operons. See Jacob–Monod hypothesis.