A repressor is a DNA-binding protein that regulates the expression of one or more genes by decreasing the rate of transcription. This blocking of expression is called repression.

Repressor proteins are coded for by regulator genes. Repressor proteins then attach to a DNA segment known as the operator. By binding to the operator, the repressor protein prevents the RNA polymerase from creating messenger RNA.

If an inducer, a molecule that initiates the gene expression, is present, then it binds to the repressor protein and deattaches it from the operator. The RNA polymerase then can create the messenger RNA and allow the gene to be expressed.

The repressor is a type of a feedback mechanism because it forces activation to occur only if a certain condition is present: the presence of inducers. Otherwise, the RNA polymerase is unable to create any RNA, conserving energy.

Gene expression

Repressor