RNA polymerase I is a type of RNA polymerase in eukaryotes responsible for synthesizing ribosomal RNA (rRNA). It is primarily composed of 14 subunits, including two large catalytic subunits and several auxiliary subunits. RNA polymerase I is mainly located in the nucleolus of the cell nucleus, specifically tasked with synthesizing a large amount of 45S precursor rRNA, which is subsequently cleaved and modified to form mature 18S, 5.8S, and 28S rRNAs. These rRNAs are essential components of the ribosome. The activity of RNA polymerase I is regulated by various factors, including phosphorylation, dephosphorylation, and growth factor signaling. Its dysfunction may affect ribosome biosynthesis and cell proliferation.