Which Eukaryotic RNA polymerase is responsible for synthesizing large rRNAs?

RNA polymerase I is specifically responsible for synthesizing large rRNAs, which are crucial components of the ribosomes. This polymerase transcribes the genes encoding the precursor of ribosomal RNA (rRNA) in eukaryotic cells, leading to the production of 28S, 18S, and 5.8S rRNA, integral for ribosome assembly and function.

In contrast, RNA polymerase II primarily transcribes protein-coding genes, producing messenger RNA (mRNA) and certain small nuclear RNAs. RNA polymerase III is involved in synthesizing small RNAs, including transfer RNA (tRNA) and some small rRNAs, but its function does not encompass the production of large rRNAs. RNA polymerase IV, found primarily in plants, is involved in the synthesis of small interfering RNAs and is not a major player in rRNA synthesis.

Thus, the specific role of RNA polymerase I in synthesizing large rRNAs highlights its essential function in ribosome production and overall protein synthesis in eukaryotic cells.