Figure 1.

Process of promoters in transcription. (A) The gene is essentially turned off. The repressor is not inhibited by lactose and binds to operator, then promoter is bound to make lactase; (B) the gene is turned on. The repressor is inhibited by lactose, then the promoter is bound by the RNA polymerase and express the genes to synthesize lactase. Finally, the lactase will digest all of the lactose, until nothing binds to the repressor. The repressor will then bind to the operator, stopping the manufacture of lactase.