Component of the 20S core proteasome complex involved in the proteolytic degradation of most intracellular proteins (PubMed:27528192). This complex plays numerous essential roles within the cell by associating with different regulatory particles (By similarity). Associated with two 19S regulatory particles, forms the 26S proteasome and thus participates in the ATP-dependent degradation of ubiquitinated proteins (By similarity). The 26S proteasome plays a key role in the maintenance of protein homeostasis by removing misfolded or damaged proteins that could impair cellular functions, and by removing proteins whose functions are no longer required (By similarity). Cleavage of peptide bonds with very broad specificity. The 26S proteasome consists of a 20S proteasome core and two 19S regulatory subunits. The 20S proteasome core is composed of 28 subunits that are arranged in four stacked rings, resulting in a barrel-shaped structure. The two end rings are each formed by seven alpha subunits, and the two central rings are each formed by seven beta subunits. The catalytic chamber with the active sites is on the inside of the barrel. No visible phenotype. Constitutive skn-1-dependent expression of the proteasomal subunit rpt-3. Double knockout with ddi-1, sel-1, sel-9, png-1 or skn-1a results in failed expression of the proteasomal subunit rpt-3. Belongs to the peptidase T1B family.