Proteasome (prosome, macropain) 26S subunit, non-ATPase, 3 (PSMD3) is a subunit of the 26S proteasome, 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. PSMD3 is a member of the proteasome subunit S3 family that functions as one of the non-ATPase subunits of the 19S regulator lid [taken from NCBI Entrez Gene (Gene ID: 5709)].