This is an example for prokaryotic gene regulation. the first described gene regulation.

•Enzyme induction is a process in which a molecule (e.g., a drug) induces (i.e., initiates or enhances) the expression of an enzyme.

•The induction of heat shock proteins in the fruit fly Drosophila melanogaster.

•The Lac operon is an interesting example of how gene expression can be regulated.

•Viruses, despite having only a few genes, possess mechanisms to regulate their gene expression, typically into an early and late phase, using collinear systems regulated by anti-terminators (lambda phage) or splicing modulators (HIV).

•Gal4 is a transcriptional activator that controls the expression of GAL1, GAL7, and GAL10 (all of which code for the metabolic of galactose in yeast). The GAL4/UAS system has been used in a variety of organisms across various phyla to study gene expression.

•A number of lactose derivatives or analogs have been described that are useful for work with the lac operon. These compounds are mainly substituted galactosides, where the glucose moiety of lactose is replaced by another chemical group.

Isopropyl-β-D-thiogalactopyranoside (IPTG) is frequently used as an inducer of the lac operon for physiological work. IPTG binds to repressor and inactivates it, but is not a substrate for β-galactosidase

•Phenyl-β-D-galactose (phenyl-Gal) is a substrate for β-galactosidase, but does not inactivate repressor and so is not an inducer. Since wild type cells produce very little β-galactosidase, they cannot grow on phenyl-Gal as a carbon and energy source

•Thiomethyl galactosidase [TMG] is another lactose analog. These inhibit the lacI repressor.  Allolactose is an isomer of lactose and is the inducer of the lac operon. Lactose is galactose-(β1->4)-glucose, whereas allolactose is galactose-(β1->6)-glucose.