Which of the following is not a tool of recombinant DNA technology?

Options

A. Restriction enzymes
B. Cloning vectors
C. Competent host
D. Recombinant proteins

Answer

To determine which of the following is not a tool of recombinant DNA technology, we will analyze each option provided.

1. **Restriction Enzyme**:
- These enzymes are crucial in recombinant DNA technology as they cut DNA at specific sequences. They are often referred to as "molecular scissors" because they allow scientists to cut DNA into manageable pieces for further manipulation. Therefore, restriction enzymes are indeed a tool of recombinant DNA technology.

2. **Cloning Vectors**:
- Cloning vectors are small DNA molecules that can carry foreign DNA into a host cell. They are essential for the process of cloning, as they allow for the insertion and amplification of the desired DNA segment. Thus, cloning vectors are also a tool of recombinant DNA technology.

3. **Competent Host**:
- A competent host refers to a cell that is capable of taking up foreign DNA, typically through a process called transformation. This is a critical step in recombinant DNA technology, as it allows the cloned DNA to be replicated within the host. Therefore, competent hosts are also considered tools in this technology.

4. **Recombinant Protein**:
- Recombinant proteins are the products that result from the expression of recombinant DNA. They are not tools used during the process but rather the end result of the recombinant DNA technology. Thus, recombinant proteins do not serve as tools in this context.

Based on the analysis above, the correct answer is that **recombinant protein is not a tool of recombinant DNA technology**; it is a product resulting from the process.

### Final Answer:
**Recombinant protein** is not a tool of recombinant DNA technology.