Eukaryotic mRNA Processing
Unlike prokaryotes which have one RNA polymerase that makes all classes of RNA molecules, eukaryotic cells have three types of RNA polymerase (called RNA pol I, RNA pol II, and RNA pol III), and each type of RNA is made by its own polymerase:
RNA polymerase I makes ribosomal RNA (rRNA)
RNA polymerase II makes messenger RNA (mRNA)
RNA polymerase III makes transfer RNA (tRNA)