At which of the following restriction sites foreign DNA should be ligated to inactivate tetracycline gene in a vector like pBR 322

Options

A. Pvu, 1 Pst I
B. Cla I, Hindi III
C. Bam HI, Sal I
D. Puv II, Eco RI

Answer

To determine at which restriction site foreign DNA should be ligated to inactivate the tetracycline gene in a vector like pBR322, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Vector pBR322**:
- pBR322 is a plasmid vector that contains genes for antibiotic resistance, specifically for ampicillin and tetracycline. These genes serve as selectable markers.

2. **Identify the Goal**:
- The goal is to inactivate the tetracycline resistance gene by inserting foreign DNA at a specific restriction site.

3. **Recognize the Restriction Sites**:
- The important restriction sites on pBR322 include BamHI and SalI. These are locations where foreign DNA can be inserted.

4. **Insertional Inactivation Concept**:
- When foreign DNA is inserted into the tetracycline resistance gene, it disrupts the gene's function, leading to what is known as insertional inactivation. This means that the tetracycline resistance is lost.

5. **Choose the Right Restriction Site**:
- Since the question asks where to ligate the foreign DNA to inactivate the tetracycline gene, we need to choose either the BamHI or SalI site. Both of these sites can be used for ligation.

6. **Conclusion**:
- Therefore, the foreign DNA should be ligated at either the BamHI or SalI restriction site to effectively inactivate the tetracycline gene in the pBR322 vector.

### Final Answer:
The foreign DNA should be ligated at either the BamHI or SalI restriction site to inactivate the tetracycline gene in the pBR322 vector.

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