Proteasome (prosome, macropain) subunit, beta type, 3 (PSMB3) is a component of the proteasome, a multicatalytic proteinase complex with a highly ordered ring-shaped 20S core structure. The core structure 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. 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. PSMB3 is a member of the proteasome B-type family, also known as the T1B family, that is a 20S core beta subunit [taken from NCBI Entrez Gene (Gene ID: 5691)].