RNA polymerase III

RNA polymerase III is a eukaryotic RNA polymerase that transcribes several small functional RNAs, including transfer RNA and 5S ribosomal RNA. It is distinct from RNA polymerase I, which makes the large precursor of most other ribosomal RNAs, and from RNA polymerase II, which transcribes protein-coding genes and many noncoding RNAs.

In 1974, Roberto Weinmann and Robert G. Roeder compared inhibition of RNA synthesis in isolated nuclei with the characteristic inhibitor sensitivity of separated RNA polymerases. The behaviour of transfer RNA and 5S ribosomal RNA synthesis matched RNA polymerase III, assigning particular RNA products to an enzymatic activity rather than grouping all nuclear transcription together.^[ref] This division of labour explains how production of translation machinery can be regulated separately from production of messenger RNA.