In order to insert alien DNA at the site of tetracycline resistance gene in pBR322 the restriction endonuclease used can be :

Options

A. Pvu I
B. ClaI
C. SaII
D. Pst I

Answer

To determine the appropriate restriction endonuclease for inserting alien DNA at the site of the tetracycline resistance gene in the plasmid pBR322, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Context**: pBR322 is a commonly used plasmid in molecular biology that contains genes for antibiotic resistance, specifically for ampicillin (amp) and tetracycline (tet).

2. **Identify the Target Site**: The question specifies that we need to insert alien DNA at the site of the tetracycline resistance gene. This means we need to select a restriction endonuclease that can cut the plasmid at or near this specific site.

3. **Evaluate the Options**:
- **Option 1: PVU1**: This restriction enzyme is used for inserting DNA at the ampicillin resistance gene, not the tetracycline site. Therefore, this option is incorrect.
- **Option 2: CLAV-1**: This enzyme is also not suitable for the tetracycline resistance site, making this option incorrect.
- **Option 3: SA-2**: This is the correct restriction endonuclease to use for inserting alien DNA at the tetracycline resistance gene site.
- **Option 4: PST1**: Similar to PVU1, this enzyme is used for the ampicillin resistance gene, thus this option is incorrect.

4. **Conclusion**: The correct restriction endonuclease to use for inserting alien DNA at the site of the tetracycline resistance gene in pBR322 is **SA-2**.

### Final Answer:
The restriction endonuclease used to insert alien DNA at the site of the tetracycline resistance gene in pBR322 is **SA-2**.