Repressor

Definition

A repressor is a protein that binds to the operator region of an operon, inhibiting transcription by preventing RNA polymerase from attaching to the promoter. Repressors play a crucial role in the regulation of gene expression in prokaryotes.

5 Must Know Facts For Your Next Test

1. Repressors bind to specific DNA sequences called operators.
2. The binding of a repressor to an operator prevents RNA polymerase from initiating transcription.
3. Repressors can be allosterically regulated by molecules such as inducers or corepressors.
4. In the lac operon, the lac repressor inhibits transcription in the absence of lactose.
5. Mutations in repressor genes can lead to constitutive expression or permanent repression of target genes.

Review Questions

• What is the primary function of a repressor protein?
• How does a repressor affect RNA polymerase activity?
• Name one example of an operon regulated by a repressor and describe its mechanism.

Related terms

operon:

A cluster of genes under the control of a single promoter and operated together.

inducer:

A molecule that binds to a repressor and causes it to release from the operator, allowing transcription.

corepressor: A molecule that enhances the binding of a repressor to an operator, thereby inhibiting transcription.