An operon is a group of genes including an operator, a common promoter, and one or more structural genes that are controlled as a unit to produce messenger RNA (mRNA). Operons occur primarily in prokaryotes and nematodes. They were first described by François Jacob and Jacques Monod in 1961.

The operon as a unit of transcription

An operon is a unit of transcription consisting of one or more structural genes, and two associated segments of DNA:

• an operator (the switch)
• a promoter (a binding site for the transcription enzyme).

The switch of an operon (that is, the "operator") is turned on unless a specific substance is bound to the operator. This substance is therefore called a repressor.

In summary:

• The "operator" is a DNA binding site for a repressor;
• transcription of the structural genes takes place unless a repressor is bound to the operator.

See also

• gene regulatory network
• Lac operon