First restriction enzyme was isolated from

Options

A. E. coli
B. Haemophilus influenzae
C. Pseudomonas
D. Xanthomonas

Answer

### Step-by-Step Solution

1. **Understanding Restriction Enzymes**:
- Restriction enzymes are proteins that cut DNA at specific sequences. They recognize specific nucleotide sequences within the DNA and cleave the DNA at or near these sites.

2. **Identifying the First Restriction Enzyme**:
- The first restriction enzyme to be discovered was isolated from a bacterium. The specific bacterium from which it was isolated is crucial to answering the question.

3. **Source of the First Restriction Enzyme**:
- The first restriction enzyme, known as Hind II, was isolated from the bacterium **Haemophilus influenzae**. This bacterium is significant in microbiology and genetics.

4. **Understanding the Name**:
- The name "Hind II" comes from "Haemophilus influenzae" and the "2" indicates that it was the second strain of this bacterium from which the enzyme was isolated.

5. **Conclusion**:
- Based on the information, the correct answer to the question "First restriction enzyme was isolated from" is **Haemophilus influenzae**.

### Final Answer
The first restriction enzyme was isolated from **Haemophilus influenzae**.

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