Proteasome Subunit Alpha Type 5 (PSMa5)

An essential function of a modified proteasome, the immunoproteasome, is the processing of class I MHC peptides. PSMA5 encodes a member of the peptidase T1A family, that is a 20S core alpha subunit.The cDNA encoded a 241-amino acid polypeptide. The calculated and observed molecular masses were 26 kD and 29 kD, respectively. Northern blot analysis revealed an mRNA of 1.2 kb in both human placenta and HeLa cells.The alpha subunits comprise the outer rings of the proteasome. Some alpha subunits contain a functional nuclear localization signal; proteasomes are found in both the nuclear and cytoplasmic compartments of the cell. Alpha subunits may constitute a physical barrier that limits access of cytosolic proteins into the inner proteolytic chamber.