Operon
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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:
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.