Operon
A cluster of genes transcribed into a single mRNA molecule.
An operon is a cluster of genes on a DNA strand that are all controlled by a single promoter and are transcribed as a single unit. This means the genes are either all turned on or all turned off together. The resulting mRNA is polycistronic and is typically translated directly into multiple proteins without any splicing. While operons are common in prokaryotes and in organelles like plastids that originated from bacteria, they are rare in eukaryotes, though examples exist in nematodes like *C. elegans* and in fruit flies. The concept was first introduced in a 1960 paper in the *Proceedings of the French Academy of Sciences*, and its development is regarded as a major milestone in molecular biology.
- first described
- 1960
- first operon discovered
- lac operon in E. coli
- primary occurrence
- prokaryotes (including organelles like plastids derived from bacteria)
- also found in
- some eukaryotes (e.g., C. elegans, Drosophila melanogaster) and viruses (e.g., T7 phages)
- Nobel Prize awarded for discoveries
- 1965 Nobel Prize in Physiology and Medicine to François Jacob, André Michel Lwoff, and Jacques Monod
Lore & Background
The term 'operon' was first proposed in a short paper in the Proceedings of the French Academy of Sciences in 1960. From this paper, the so-called general theory of the operon was developed, which suggested that in all cases, genes within an operon are negatively controlled by a repressor acting at a single operator located before the first gene. Later, it was discovered that genes could be positively regulated and also regulated at steps that follow transcription initiation, so it is not possible to talk of a general regulatory mechanism, because different operons have different mechanisms. The first operon to be described was the lac operon in E. coli. The 1965 Nobel Prize in Physiology and Medicine was awarded to François Jacob, André Michel Lwoff and Jacques Monod for their discoveries concerning the operon and virus synthesis.
Reader's Guide
The operon concept is a cornerstone of molecular biology, providing the first clear model of how gene expression is coordinated in cells. Originally thought to exist solely in prokaryotes, operons were later discovered in some eukaryotes in the early 1990s, though they remain rare. The lac operon in E. coli remains the classic example, illustrating negative control by a repressor and induction by allolactose. Operons can be regulated by both negative and positive control mechanisms, and different operons have different mechanisms, so no single regulatory model applies universally. The term 'operon' is derived from the verb 'to operate.' Operons are related to regulons, stimulons, and modulons, which represent different levels of gene regulation. The discovery of operons fundamentally changed understanding of gene regulation and earned its discoverers the Nobel Prize.
Did You Know?
- The term 'operon' was first proposed in a short paper in the Proceedings of the French Academy of Sciences in 1960.
- The first operon to be described was the lac operon in E. coli.
- Operons are also found in viruses such as bacteriophages; for example, T7 phages have two operons.
- The 1965 Nobel Prize in Physiology and Medicine was awarded to François Jacob, André Michel Lwoff and Jacques Monod for their discoveries concerning the operon and virus synthesis.
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