A foreign DNA and plasmid cut by the same restriction endonuclease can be joined to form a recombinant plasmid using

Options

A. Eco RI
B. Taq polymerase
C. Polymerase III
D. Ligase

Answer

To solve the question, we need to identify the correct enzyme used to join a foreign DNA and a plasmid that have been cut by the same restriction endonuclease. Here’s the step-by-step solution:

### Step 1: Understand the Components
- We have two components: foreign DNA and a plasmid.
- Both components are cut by the same restriction endonuclease, which creates compatible ends for joining.

**Hint:** Identify the components involved in the process of creating a recombinant plasmid.

### Step 2: Know the Role of Restriction Endonucleases
- Restriction endonucleases (like EcoRI) are enzymes that cut DNA at specific sequences, generating sticky or blunt ends.
- These ends can be used to facilitate the joining of different DNA fragments.

**Hint:** Recall what restriction endonucleases do and how they prepare DNA for ligation.

### Step 3: Identify the Joining Process
- To join the foreign DNA and plasmid, we need to form phosphodiester bonds between the DNA fragments.
- This is done by an enzyme that facilitates the joining of these DNA pieces.

**Hint:** Think about the enzyme that is responsible for sealing the nicks in the DNA backbone.

### Step 4: Determine the Correct Enzyme
- The enzyme that catalyzes the formation of phosphodiester bonds between the DNA fragments is DNA ligase.
- DNA ligase is specifically used to join the DNA fragments after they have been cut by restriction enzymes.

**Hint:** Consider which enzyme is commonly used in molecular biology for ligating DNA fragments together.

### Step 5: Evaluate the Options
- **Option 1: EcoRI** - This is a restriction endonuclease, so it cannot join the DNA.
- **Option 2: Taq polymerase** - This enzyme is used for DNA synthesis, not for joining.
- **Option 3: Polymerase** - This is also involved in DNA synthesis, not in joining.
- **Option 4: Ligase** - This is the correct choice as it is responsible for joining the DNA fragments.

**Hint:** Review the options carefully and eliminate those that do not perform the joining function.

### Final Answer
The correct answer is **DNA ligase**.