The first restriction endonuclease to be discovered was :

Options

A. hlnd II
B. EcoR I
C. Baan HI
D. Pst I

Answer

**Step-by-Step Solution:**

1. **Understanding Restriction Endonucleases**:
- Restriction endonucleases are enzymes that cut DNA at specific sequences. They are produced by bacteria and serve as a defense mechanism against foreign DNA, such as that from viruses.

2. **Identifying the First Discovered Restriction Endonuclease**:
- Among the various restriction enzymes, the question asks for the first one that was discovered.

3. **Considering the Options**:
- The options provided are ECO-R1, BAM-H1, and PST-1.

4. **Recalling Historical Context**:
- The first restriction enzyme to be discovered was HindII, which was isolated from the bacterium Haemophilus influenzae.

5. **Conclusion**:
- Therefore, the answer to the question is HindII.

**Final Answer**: The first restriction endonuclease to be discovered was HindII.

---