RNA+polymerase

=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.