Restriction endonuclease was isolated for the first time by W. Aber in 1962 in bacteria. Restriction endonucleases cut the DNA duplex at specific points therefore they are also called as molecular scissors or biological scissors. Three types of restriction endonuclease are Type 1. Type II and Type III but only Type II restriction endonucleases are used in recombinant DNA technology. Restriction endonuclease EcoR I recognises the base sequence GAATTC In DNA duplex and cut strands between G and A.
Which of the following ions are used by restriction endonucleases for restriction?

Options

A. `Mg^(2+)` ions
B. `Mn^(2+)` ions
C. ` Na^(+)` ions
D. `K^(+)` ions

Explanation

**Step-by-Step Solution:**

1. **Understanding Restriction Endonucleases:**
- Restriction endonucleases, also known as restriction enzymes, are proteins that cut DNA at specific sequences. They were first isolated by W. Aber in 1962 from bacteria.

2. **Types of Restriction Endonucleases:**
- There are three types of restriction endonucleases: Type I, Type II, and Type III. However, only Type II restriction endonucleases are commonly used in recombinant DNA technology.

3. **Example of a Restriction Endonuclease:**
- An example of a Type II restriction endonuclease is EcoR I, which recognizes the DNA sequence GAATTC and cuts between the G and A.

4. **Role of Ions in Restriction Endonucleases:**
- Restriction endonucleases require certain ions to function properly. The question asks which ions are used by these enzymes during the restriction process.

5. **Identifying the Correct Ion:**
- The correct ion used by restriction endonucleases is magnesium (Mg²⁺). These enzymes typically bind to two magnesium ions which are essential for their catalytic activity.

6. **Mechanism of Action:**
- One of the magnesium ions binds to the phosphate group of the DNA where the cleavage occurs, which is crucial for the enzyme's ability to cut the DNA.

7. **Conclusion:**
- Based on the information provided, the correct answer to the question is that magnesium ions (Mg²⁺) are used by restriction endonucleases for restriction.

**Final Answer: Magnesium ions (Mg²⁺).**

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