Ready-to-use ELISA kits are available for the detection of ribonuclease P 21 subunit, an alias of the protein, ribonuclease P/MRP subunit p21. The official gene symbol is RPP21. The protein, with a mass of 17.6 kDa and length of 154 residues, is reported to be nuclear. It is a member of the Eukaryotic/archaeal RNase P protein component 4 family and may be known by other names, including: CAT60, ribonucleoprotein V, ribonuclease P/MRP 21kDa subunit, RNaseP protein p21, and ribonuclease P protein subunit p21.