Which of the following transcribe 5s rRNA?
**Core Concept**
The transcription of ribosomal RNA (rRNA) is a crucial step in the synthesis of ribosomes, the cellular machinery responsible for protein synthesis. In eukaryotic cells, the 5S rRNA is transcribed by a specialized RNA polymerase, which is distinct from the RNA polymerase II responsible for transcribing messenger RNA (mRNA) and other types of RNA.
**Why the Correct Answer is Right**
The correct answer, **C. RNA polymerase III**, is responsible for transcribing the 5S rRNA gene in eukaryotic cells. This enzyme is specific to the transcription of 5S rRNA, tRNA, and other small RNA molecules. The transcription of 5S rRNA by RNA polymerase III is a highly regulated process that involves the assembly of a preinitiation complex and the recruitment of the enzyme to the 5S rRNA gene. The 5S rRNA gene is a single-copy gene located in the nucleolar organizer region of the chromosome.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it refers to RNA polymerase I, which is responsible for transcribing the 28S, 18S, and 5.8S rRNA genes in eukaryotic cells.
* **Option B:** This option is incorrect because it refers to RNA polymerase II, which is responsible for transcribing messenger RNA (mRNA) and other types of RNA, but not 5S rRNA.
**Clinical Pearl / High-Yield Fact**
The 5S rRNA gene is a single-copy gene, and its transcription is tightly regulated to ensure proper ribosome biogenesis. Mutations in the 5S rRNA gene or its promoter region can lead to ribosome biogenesis disorders, which can have severe consequences for cellular function and overall health.
**Correct Answer:** C. RNA polymerase III.