The linking of alien DNA to plasmid vector is possible with the help of :

Options

A. Taq polymerase
B. DNA ligase
C. polyethylene glycol
D. restriction endonuclease type II

Answer

To solve the question about the linking of alien DNA to a plasmid vector, we need to analyze the options provided and understand the role of each enzyme or compound mentioned.

### Step-by-Step Solution:

1. **Understanding Alien DNA and Plasmid Vector**:
- Alien DNA refers to any foreign DNA that is introduced into an organism. In this context, it is the DNA that we want to insert into a plasmid vector.
- A plasmid vector is a small, circular piece of DNA that can replicate independently within a host cell and is used to carry foreign DNA into a target cell.

2. **Identifying the Process**:
- To link alien DNA to a plasmid vector, we need to cut the plasmid at specific sites and then insert the alien DNA into these sites. This process involves two main steps: cutting the DNA and then joining the DNA fragments.

3. **Analyzing the Options**:
- **Tag Polymerase**: This enzyme is primarily used in the polymerase chain reaction (PCR) for DNA amplification. It does not play a role in linking DNA fragments.
- **DNA Ligase**: This enzyme is crucial for joining two DNA fragments together. It catalyzes the formation of phosphodiester bonds between the 3' hydroxyl end of one DNA fragment and the 5' phosphate end of another. This is the enzyme that links the alien DNA to the plasmid vector.
- **Polyethylene Glycol**: This is a compound used in various applications, including as a precipitating agent in molecular biology, but it does not directly link DNA fragments.
- **Restriction Endonuclease Type 2**: These enzymes are used to cut DNA at specific sequences, which is essential for preparing the plasmid and alien DNA for ligation. However, they do not join the DNA fragments.

4. **Conclusion**:
- The linking of alien DNA to a plasmid vector is accomplished by **DNA ligase**. This enzyme facilitates the joining of the alien DNA with the plasmid vector after the plasmid has been cut by restriction endonucleases.

### Final Answer:
The linking of alien DNA to plasmid vector is possible with the help of **DNA ligase**.

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