Final answer:
The lacI gene produces a repressor protein that regulates the lac operon in E. coli. It prevents the transcription of genes for lactose metabolism when lactose is not present but allows it when lactose is available and glucose is scarce.
Step-by-step explanation:
The product of the lacI gene is the repressor protein. This repressor binds to the operator site in the lac operon, a set of genes involved in lactose metabolism in E. coli. When no lactose is present, the repressor protein effectively blocks transcription of the operon by binding to the operator, preventing RNA polymerase from transcribing the downstream genes lacZ, lacY, and lacA.
However, when lactose is present and glucose levels are low, lactose is converted to allolactose, which acts as an inducer by binding to the repressor. This causes a conformational change in the repressor, releasing it from the operator and allowing transcription to proceed. The lacZ gene encodes β-galactosidase, which breaks down lactose, while lacY encodes lactose permease, a transport protein, and lacA encodes a transacetylase whose role is less understood.