RNA polymerase

RNA polymerases are a family of enzymes involved in RNA synthesis, most notably in transcription (i.e. they are transcriptases).

Prokaryotic RNA polymerase is the single multi-domain enzyme responsible for both mRNA and ncRNA (non-coding RNA) synthesis in prokaryotes. It has multiple subunits: two alpha subunits, which assemble the enzyme and bind the rest of the polymerase; a beta subunit, which catalyses the synthesis of RNA; a beta-prime subunit, which binds nonspecifically to DNA; and an omega subunit which offers a protective, chaperone function to the beta-prime subunit in vivo (it also restores denatured RNA polymerase in vitro).

Eukaryotic RNA polymerases come in three main types:

  1. RNA Polymerase I is found in the nucleolus and is responsible for synthesising ribosomal RNA (rRNA). It is detectable by its insensitivity to the toxin alpha-Amanitin
  2. RNA Polymerase II is found in the nucleoplasm and is responsible for synthesising messenger RNA (mRNA; specifically pre-mRNA), and most snRNA and microRNA. It is highly sensitive to alpha-Amanitin, making this a deadly toxin.
  3. RNA Polymerase III is also found in the nucleoplasm and is responsible for synthesising transfer RNA (tRNA), 5S rRNA and other small RNAs. It is of intermediate sensitivity to alpha-Aminitin.