The 26S proteasome is a multicatalytic proteinase complex
with a highly ordered structure composed of 2 complexes, a 20S core
and a 19S regulator. The 20S core is composed of 4 rings of 28
non-identical subunits; 2 rings are composed of 7 alpha subunits
and 2 rings are composed of 7 beta subunits. The 19S regulator is
composed of a base, which contains 6 ATPase subunits and 2
non-ATPase subunits, and a lid, which contains up to 10 non-ATPase
subunits. Proteasomes are distributed throughout eukaryotic cells
at a high concentration and cleave peptides in an
ATP/ubiquitin-dependent process in a non-lysosomal pathway. An
essential function of a modified proteasome, the immunoproteasome,
is the processing of class I MHC peptides. This gene encodes one of
the non-ATPase subunits of the 19S regulator lid. Pseudogenes have
been identified on chromosomes 10 and 21.
