DNA transcription uses three polymerase enzymes – RNA polymerase I, RNA polymerase II, and RNA polymerase III. Although the structures of all three polymerase enzymes are homologous, they perform different functions. 

RNA polymerase I plays a role in the transcription of ribosomal RNA. It is located in the nucleolus. 

RNA polymerase II is located in the nucleus and plays a role in the transcription of mRNA. 

RNA polymerase III is also located in the nucleus and is responsible for the transcription of both ribosomal RNA and transfer RNA.