The precursor of mRNA is transcribed by

Options

A. RNA polymerase I
B. RNA polymerase II
C. RNA polymerase III
D. Topoisomerase

Answer

To solve the question "The precursor of mRNA is transcribed by," we need to identify which RNA polymerase is responsible for transcribing the precursor mRNA (also known as pre-mRNA) in eukaryotic cells.

### Step-by-Step Solution:

1. **Understand the Role of RNA Polymerases**:
- There are three main types of RNA polymerases in eukaryotic cells: RNA polymerase I, RNA polymerase II, and RNA polymerase III.
- Each of these polymerases has a specific function in the transcription of different types of RNA.

2. **Identify the Function of Each RNA Polymerase**:
- **RNA Polymerase I**: Primarily transcribes ribosomal RNA (rRNA), except for 5S rRNA.
- **RNA Polymerase II**: Transcribes messenger RNA (mRNA) and some small nuclear RNAs (snRNA).
- **RNA Polymerase III**: Transcribes transfer RNA (tRNA), 5S rRNA, and other small RNAs.

3. **Determine the Precursor of mRNA**:
- The precursor of mRNA is known as pre-mRNA, which is synthesized from the DNA template during the process of transcription.
- Pre-mRNA undergoes processing to become mature mRNA.

4. **Identify the Correct RNA Polymerase**:
- Since pre-mRNA is transcribed from DNA, we need to identify which RNA polymerase is responsible for this process.
- RNA polymerase II is specifically responsible for the transcription of pre-mRNA in eukaryotic cells.

5. **Select the Correct Answer**:
- Based on the functions of the RNA polymerases, the correct answer to the question is **RNA polymerase II** (Option 2).

### Final Answer:
The precursor of mRNA is transcribed by **RNA polymerase II**.

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