opérons

Opérons is the French plural of opéron, a genetic regulatory unit found in prokaryotes that coordinates the transcription of a cluster of functionally related genes. The concept, central to the operon model proposed by François Jacob and Jacques Monod in 1961, illustrates how bacteria adjust gene expression in response to environmental changes.

Structure: An opéron typically includes a promoter, an operator, and a contiguous set of structural genes that are transcribed together into a single polycistronic mRNA. A regulatory gene, often distant from the operon, encodes a repressor protein that can bind to the operator and block transcription.

Regulation: Operons can be inducible or repressible. Inducible operons are usually off until an inducer binds the repressor, allowing transcription (for example, the lac operon in Escherichia coli). Repressible operons are usually on but repressed when a corepressor (for instance, tryptophan) binds the repressor, reducing transcription. Positive regulation can occur when a regulator such as CAP–cAMP enhances transcription in response to cellular conditions.

Distribution and significance: Operons are common in bacteria and some archaea, enabling coordinated control of metabolic pathways. In contrast, most eukaryotic genes are not organized into operons; regulation tends to be individual and more complex. The operon concept remains foundational in molecular biology and has influenced biotechnology and synthetic biology, including the design of engineered gene circuits.