In lac operon,the regulator gene codes for

Options

A. Aporepressor
B. Corepressor
C. Inactive repressor
D. Active repressor

Answer

### Step-by-Step Solution:

1. **Understanding the Lac Operon**: The lac operon is a genetic system found in E. coli that is responsible for the metabolism of lactose. It consists of structural genes, a promoter, an operator, and a regulator gene.

2. **Identifying the Regulator Gene**: The regulator gene in the lac operon is known as the "i" gene (inhibitor gene). This gene codes for a protein that acts as a repressor.

3. **Function of the Repressor**: The repressor protein synthesized by the regulator gene binds to the operator region of the operon. When the repressor is bound to the operator, it prevents RNA polymerase from transcribing the structural genes (Z, Y, A) needed for lactose metabolism.

4. **Role of Inducer (Lactose)**: In the absence of lactose (the inducer), the repressor remains active and binds to the operator, blocking transcription. When lactose is present, it binds to the repressor, causing a conformational change that inactivates the repressor. This allows RNA polymerase to transcribe the structural genes.

5. **Conclusion**: Therefore, the regulator gene in the lac operon codes for the active repressor, which is crucial for controlling the expression of the genes involved in lactose metabolism.

### Final Answer:
The regulator gene in the lac operon codes for the **active repressor**.

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