In eukaryotes , which of these rRNA is not synthesized by RNA Polymerase I ?

Options

A. 28S rRNA
B. 5S rRNA
C. 5.8S rRNA
D. 18S rRNA

Answer

To determine which ribosomal RNA (rRNA) is not synthesized by RNA Polymerase I in eukaryotes, we need to understand the roles of the different RNA polymerases in the synthesis of rRNA.

### Step-by-Step Solution:

1. **Identify the Types of RNA Polymerases**:
- In eukaryotic cells, there are three main types of RNA polymerases:
- RNA Polymerase I
- RNA Polymerase II
- RNA Polymerase III

2. **Functions of RNA Polymerases**:
- **RNA Polymerase I**: This polymerase is responsible for synthesizing the precursor of ribosomal RNA (pre-rRNA), which includes 18S, 5.8S, and 28S rRNA.
- **RNA Polymerase II**: This polymerase synthesizes messenger RNA (mRNA) and some specialized RNAs.
- **RNA Polymerase III**: This polymerase synthesizes transfer RNA (tRNA), 5S rRNA, and other small RNAs.

3. **List the Options**:
- The options provided are:
- 28S rRNA
- 5S rRNA
- 5.8S rRNA
- 18S rRNA

4. **Analyze Each Option**:
- **28S rRNA**: Synthesized by RNA Polymerase I.
- **5S rRNA**: Synthesized by RNA Polymerase III (not by RNA Polymerase I).
- **5.8S rRNA**: Synthesized by RNA Polymerase I.
- **18S rRNA**: Synthesized by RNA Polymerase I.

5. **Conclusion**:
- Since 5S rRNA is the only ribosomal RNA listed that is synthesized by RNA Polymerase III and not by RNA Polymerase I, the correct answer is **5S rRNA**.

### Final Answer:
**5S rRNA**