RNA polymerase I is primarily responsible for the transcription of which of the following?

RNA polymerase I is specifically responsible for the transcription of ribosomal RNA (rRNA). In eukaryotes, this type of RNA is essential for the formation of ribosomes, which are the cellular machinery that synthesizes proteins. RNA polymerase I synthesizes the precursor of rRNA, which is then processed into the various components of ribosomes, including 18S, 5.8S, and 28S rRNA.

The function of RNA polymerase I is distinct from other types of RNA polymerases. For example, RNA polymerase II transcribes messenger RNA (mRNA), which serves as the template for protein synthesis, while RNA polymerase III is responsible for the transcription of transfer RNA (tRNA) and small nuclear RNA (snRNA). Understanding these specific roles helps clarify the unique contributions of each RNA polymerase in the process of gene expression and the overall functioning of the cell.