inducer

…results from the addition of inducers—usually compounds that exhibit some structural similarity to the substrates on which the enzymes act. A classic example of an inducible enzyme of this type is β-galactosidase. Escherichia coli growing in nutrient medium containing glucose do not utilize the milk sugar, lactose (glucose-4-β-d-galactoside); however, if…

…operons: a molecule called an inducer can bind to the repressor, inactivating it; or a repressor may not be able to bind to the operator unless it is bound to another molecule, the corepressor. Some operons are under attenuator control, in which transcription is initiated but is halted before the…

…present, it acts as an inducer by combining with the repressor so as to prevent its binding to DNA. As a result, the enzyme is synthesized; i.e., its formation by the microorganism is induced.