Which of the following is not a restriction endonuclease ?

Options

A. Eco RI
B. Hind III
C. Pst I
D. DNase I

Answer

To solve the question of which of the following is not a restriction endonuclease, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Terms**:
- **Restriction Endonuclease**: These are enzymes that cut DNA at specific sequences. They are a type of nuclease, which are enzymes that cut nucleic acids (DNA or RNA).
- **Exonuclease vs. Endonuclease**: Exonucleases remove nucleotides from the ends of a DNA molecule, while endonucleases cut within the DNA strand at specific sites.

2. **List the Options**:
- The options given are:
1. ECO-R1
2. HIN-3
3. PST-1
4. DNS-1

3. **Identify Each Enzyme**:
- **ECO-R1**: This is a well-known restriction endonuclease that cuts DNA at specific sequences.
- **HIN-3**: This is also a restriction endonuclease.
- **PST-1**: This is another restriction endonuclease.
- **DNS-1**: This is identified as an exonuclease, which means it does not cut DNA in the same manner as the restriction endonucleases.

4. **Determine the Correct Answer**:
- Since DNS-1 is an exonuclease and does not function as a restriction endonuclease, the correct answer to the question is **Option 4: DNS-1**.

### Final Answer:
**DNS-1 is not a restriction endonuclease.**

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