Operator (biology)

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Top: The operator is shown in red, part of the DNA. It is bound to the repressor (green), which prevents RNA polymerase (yellow) from transcribing the target genes (6,7,8). Bottom: The green repressor is inhibited by the white molecule. RNA polymerase (yellow) is free to transcribe the target genes (6,7,8). This particular process shows the operator's role in the lac operon. Lactose is the white molecule in the bottom diagram.

In genetics, an operator is a segment of DNA to which a transcription factor binds to regulate gene expression. The transcription factor is typically a repressor, which can bind to the operator to prevent transcription.

The operator is classically defined in the lac operon to be located between the promoter and the target genes.


In the case of a repressor, the repressor protein physically obstructs the RNA polymerase from transcribing the genes. An inducer (protein) can displace a repressor (protein) from the operator site (DNA), which results in an uninhibited operon.