Final answer:
RNA polymerase I is responsible for the synthesis of pre-rRNA in eukaryotes. It transcribes precursor molecules that are then processed to form mature rRNA for ribosome function.
Step-by-step explanation:
In eukaryotes, the pre-rRNA is synthesized by a specific enzyme known as RNA polymerase I. This polymerase is essential for transcribing the large rRNA precursor molecules, such as the 45S precursor, that include the 5.8S, 18S, and 28S rRNA components. These precursor molecules then undergo extensive processing, including cleavage, splicing, methylation, and sometimes chemical conversion, to form the mature rRNA necessary for ribosome function. The enzyme is located in the nucleus and catalyzes the synthesis of most RNA in a eukaryotic cell, especially the rRNAs, which are crucial components of the protein synthesis machinery.