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Concept 4: The lac Regulatory Gene

The regulatory gene lacI produces an mRNA that produces a Lac repressor protein, which can bind to the operator of the lac operon.

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In some texts, the lacI regulatory gene is called the lacI regulator gene. Regulatory genes are not necessarily close to the operons they affect.

The general term for the product of a regulatory gene is a regulatory protein. The Lac regulatory protein is called a repressor because it keeps RNA polymerase from transcribing the structural genes. Thus the Lac repressor inhibits transcription of the lac operon.