What is the difference between RNA polymerase I and II?

RNA polymerase I and RNA polymerase II are two types of eukaryotic RNA polymerases that perform distinctly different functions during transcription.

RNA polymerase I

• Is a 590 kDa enzyme
• Comprised of 14 protein subunits
• Contain the same 2 non-identical α-like subunits
• Located in the nucleolus
• Transcribes rRNA genes
• Is responsible for producing 50% of the total RNA of the cell
• Is insensitive to α-amanitin
• Promoters sequences vary considerably from one species to another

RNA polymerase II:

• Is a 550 kDa enzyme
• Comprised of 12 protein subunits
• Contains two copies of a different α-like subunit
• Located in the nucleoplasm
• Transcribes mRNA, miRNA, snRNA, and snoRNA genes
• Is sensitive to 1 μg/mL α-amanitin
• Several promoters have a few sequences in common