Explanation
In E. coli, the lac operon is induced by lactose. Therefore, the answer is A) Lactose.
The lac operon is a cluster of genes in E. coli that are involved in the metabolism of lactose. It consists of three structural genes: lacZ, lacY, and lacA, which encode for the proteins β-galactosidase, lactose permease, and transacetylase respectively. These genes are under the control of a promoter, operator, and regulatory genes.
The lac operon is regulated by the lac repressor, which binds to the operator site and inhibits transcription of the structural genes. In the presence of lactose, it acts as an inducer and binds to the repressor, causing it to detach from the operator and allowing RNA polymerase to initiate transcription. Therefore, lactose induces the expression of the lac operon in E. coli by alleviating the repression of the lac repressor.
