operon, in genetics, site on a bacterial chromosome containing genes that control protein synthesis (structural genes) together with a gene that determines whether the structural genes are active or not (operator gene). See nucleic acid.

Genetic regulatory system of single-celled organisms (prokaryotes) and their viruses, in which genes coding for functionally related proteins are clustered along the DNA, enabling their expression to be coordinated in response to the cell's needs. By providing a means to produce proteins only when and where they are required, the operon allows the cell to conserve energy. A typical operon consists of a group of structural genes that code for enzymes involved in a metabolic pathway, such as the biosynthesis of an amino acid. A single unit of messenger RNA is transcribed from the operon and is then translated into separate proteins. Operons are controlled by various regulatory elements that respond to environmental cues. The operon system was first proposed by Franchooklois Jacob and Jacques Monod in the early 1960s.

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