Acts as a regulatory subunit of the 26 proteasome which is involved in the ATP-dependent degradation of ubiquitinated proteins. Component of the 19S regulatory particle (RP/PA700) lid subcomplex of the 26S proteasome. The 26S proteasome is composed of a core protease (CP), known as the 20S proteasome, capped at one or both ends by the 19S regulatory particle (RP/PA700). The RP/PA700 complex is composed of at least 17 different subunits in two subcomplexes, the base and the lid, which form the portions proximal and distal to the 20S proteolytic core, respectively (PubMed:14623884, PubMed:20516081). Interacts with UCH1 and UCH2 (PubMed:22951400). Ubiquitous with highest expression in flowers. Short pollen tube growth and failure to exit the style. Belongs to the proteasome subunit S3 family.