In negative operon

Options

A. Inducer binds to repressor
B. Inducer binds to corepressor
C. Corepressor binds to aporepressor
D. A repressor is not formed

Answer

### Step-by-Step Solution:

1. **Understanding Negative Operon**:
- A negative operon is a type of operon that is regulated by a repressor protein. This means that the repressor can bind to the operator region of the operon and inhibit transcription.

2. **Role of Inducers**:
- An inducer is a small molecule that can regulate gene expression. It typically binds to a repressor protein, causing a change in the repressor's shape (conformation) that prevents it from binding to the operator.

3. **Example of Negative Operon - Lac Operon**:
- The lac operon in E. coli is a classic example of a negative inducible operon. In the absence of lactose (the inducer), the repressor is active and binds to the operator, blocking transcription of the genes required for lactose metabolism.

4. **Inducer Binding**:
- When lactose is present, it acts as an inducer by binding to the repressor protein. This binding causes a conformational change in the repressor, which then cannot bind to the operator.

5. **Result of Inducer Binding**:
- As a result of the repressor being unable to bind to the operator, RNA polymerase can access the promoter region and initiate transcription of the genes needed for lactose metabolism.

6. **Conclusion**:
- Therefore, in the context of the negative operon, the correct statement is that the inducer binds to the repressor, leading to the inactivation of the repressor and allowing gene expression to occur.

### Final Answer:
- The correct option is: **Inducer binds to the repressor.**

---