Rejoining of vector molecule after restriction enzyme digestion can be avoided by

Options

A. Using different enzymes for insert and vector
B. Using same enzyme for insert and vector
C. Using DNA ligase immediately after digestion
D. Using alkaline phosphatase on only vector

Answer

To solve the question regarding how to avoid the rejoining of a vector molecule after restriction enzyme digestion, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Self-Ligation**:
- After a vector is cut by restriction enzymes, it can potentially rejoin itself. This process is known as self-ligation, where the sticky ends of the vector can come together and circularize again.

2. **Identify the Problem**:
- The main issue is that when the vector is digested, it can rejoin itself instead of allowing for the insertion of the desired DNA fragment. This can lead to unsuccessful cloning experiments.

3. **Explore Solutions**:
- To prevent self-ligation, we need to modify the vector in such a way that it cannot circularize after being cut.

4. **Consider the Options**:
- **Using Different Enzymes for Insert and Vector**: This would not prevent self-ligation of the vector itself.
- **Using Same Enzymes for Insert and Vector**: This would still allow for self-ligation.
- **Using DNA Ligase Immediately After Digestion**: This would promote ligation rather than prevent it.
- **Using Alkaline Phosphatase Only on Vectors**: This option involves treating the vector with alkaline phosphatase, which removes the phosphate groups from the ends of the vector, preventing the formation of phosphodiester bonds necessary for self-ligation.

5. **Conclude the Best Approach**:
- The most effective method to avoid the rejoining of the vector molecule after restriction enzyme digestion is to use alkaline phosphatase only on the vector. This treatment dephosphorylates the ends of the vector, preventing it from self-ligating.

### Final Answer:
Rejoining of the vector molecule after restriction enzyme digestion can be avoided by using alkaline phosphatase only on vectors.

---