PSMA1 (Proteosome subunit alpha type-1; also 30kD prosomal protein/PROS30, HC2, proteasome component C2/PSC2, PSMA-1/alpha6, and NU) is a 30kD member of the peptidase T1A family of enzymes. It is widely expressed, and found in both cytoplasm and nucleus. Short-lived intracellular molecules (typically proteins) are enzymatically degraded by the 26S proteosome. This is a multisubunit 3D complex that is over 2000kD in size, and recognizes previously ubiquitinated proteins. The middle of this 26S complex is shaped like a barrel with four staves that run circumferentially rather than longitudinally. Each stave contains seven subunits, with beta-type subunits generating the two center staves, and alpha-type subunits comprising the outer, or flanking staves. The function of the barrel, also known as the 20S protease core "particle", is to enzymatically cleave substrates that enter its chamber. For proteins, this is done by beta-type subunits. The 26S complex also cleaves mRNA, and this is mediated by alpha-type subunits. PSMA-1/alpha6 does not cleave mRNA, but it does positively regulate PSMA5/alpha5 catalytic activity. Notably, PSMA1 has also been reported to bind to LPS. Human PSMA1 is 263 amino acids (aa) in length. It contains an acetylated Met at position #1, plus three utilized phosphorylation sites at Tyr6, Thr11, and Ser16. There are at least four potential isoform variants. Three utilize alternative start sites. One shows a start site at Met140, while a second and third initiates translation at sites 6 and 43aa upstream of the standard site, respectively. A fourth isoform possess a 16aa substitution for aa115-263. Over aa16-263, human PSMA1 shares 98% aa sequence identity with mouse PSMA1.