An operon is a sequence of DNA containing a cluster of genes under the control of a single promoter

  • Hence, genes within an operon will always be expressed together or not at all (their expression patterns are linked)

There are three basic components to an operon

  • Promoter – Upstream sequence to which RNA polymerase binds
  • Operator – Segment of DNA to which a repressor protein binds (inhibits transcription by obstructing RNA polymerase)
  • Structural genes – Genes that are collectively regulated by the operon

Operons are related to stimulons and regulons:

  • Stimulon – Set of genes under regulation from a single cell stimulus
  • Regulon – Set of genes under regulation from a single regulatory protein (each gene has a different operator though)

Originally, operons were thought to exist only in prokaryotes, however examples have since been found in eukaryotes

Structure of an Operon