If lactose is not available in the cell, the lac operon remains in a repressed state, and the expression of the lacI gene is unaffected. The lacI gene encodes the lac repressor protein, which is responsible for regulating the lac operon.
In the absence of lactose, the lac repressor protein binds to the operator region of the lac operon, preventing the RNA polymerase from transcribing the structural genes (lacZ, lacY, and lacA). This binding of the lac repressor to the operator effectively represses the expression of the lac operon.
The lac repressor protein acts as a transcriptional repressor, meaning it inhibits gene expression by blocking the initiation of transcription. It does so by binding to a specific DNA sequence, the operator, located near the promoter region of the lac operon.
Therefore, if lactose is not available in the cell, the lac repressor remains bound to the operator, blocking the RNA polymerase from transcribing the genes of the lac operon, including the lacI gene itself. As a result, the expression of the lacI gene remains at a basal level, allowing the lac repressor to continue repressing the lac operon until lactose becomes available.