Gene regulation governing lactose operon of E.coli that involves the lac I gene product is

When lactose is absent from the medium the repressor protein binds to the operator region of the operon and prevents RNA polymerase from transcribing the operon. Regulation of lac operon by repressor is referred to as negative regulation. In the absence of a preferred carbon source such as glucose, if lactose is provided in the growth medium of the bacteria, the lactose is transported into the cells through the action of permease. In the presence of an inducer, such as lactose or allolactose, the repressor is inactivated by interaction with the inducer. This allows RNA polymerase access to the promoter and transcription proceeds. This shows that the operon is inducible which reflects the role of substrate and its involvement in enzyme production.