The lactose operon in E. coli is the group of genes that regulates the production of enzymes necessary to break down lactose in bacterial cells.
It is an example of an inducible operon in which the presence of a key metabolic substance (lactose, an alternative energy source) induces the transcription of structural genes.
- If lactose is present in the medium, the lactose molecule functions as a signal molecule, as it binds to the repressor, making it unable to bind to the operator.
- In the absence of lactose, the system works by allowing the expression of the regulatory gene, which synthesizes a protein that binds to the operator.
This binding incapacitates the RNA polymerase, located on the promoter, to read the DNA and carry out the transcription of the structural genes and consequently the transcription of the operon is turned off.
- It is said that there is a repression at the transcriptional level and the protein encoded by the regulatory gene is called the repressor protein.
Therefore, we can conclude that the lactose (lac) operon in E. coli is an example of a gene that is repressed when lactose is not available in a cell.
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