Acts as a regulatory subunit of the 26S proteasome which is involved in the ATP-dependent degradation of ubiquitinated proteins. The 26S proteasome is composed of a core protease, known as the 20S proteasome, capped at one or both ends by the 19S regulatory complex (RC). The RC is composed of at least 18 different subunits in two subcomplexes, the base and the lid, which form the portions proximal and distal to the 20S proteolytic core, respectively (By similarity). N-acetylated by NAT1. Present with 16700 molecules/cell in log phase SD medium. Belongs to the proteasome subunit S3 family.