The action of the repressor on the expression of the lac operon is an example of negative control.
Operon: A set of genes transcribed under the control of an operator gene. More specifically, an operon is a segment of DNA containing adjacent genes including structural genes, an operator gene, and a regulatory gene. An operon is thus a functional unit of transcription and genetic regulation.Both mechanisms are present in the lac operon. Because expression is often restricted by an active repressor (the lac repressor) that turns off transcription, it is a negative control system. The lac repressor attaches to the operator region and inhibits transcription from taking place.
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