AAT Bioquest

What is the difference between RNA polymerase I and II?

Posted October 28, 2021


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
Additional resources

Comparative overview of RNA polymerase II and III transcription cycles, with focus on RNA polymerase III termination and reinitiation

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