The lac operon consists of one regulatory gene and three structural genes (z, y, and a)T the I gene codes for the repressor of the lac. If repressor protein binds to the operator region of the operon, it prevents RNA polymerase from transcribing the operon. Whereas, in presence of lactose (inducer) the repressor becomes inactivated due to interaction with the inducer. This allows RNA polymerase access to promoter and transcription proceeds. Regulation of lac operon is negative. Regulation of lac operon by a repressor is referred to as negative regulation.