Acts as a regulatory subunit of the 26 proteasome which is involved in the ATP-dependent degradation of ubiquitinated proteins. Transcription factor pap1 is controlled by the functional interaction between the positive regulator pad1 and negative regulator crm1. Both these proteins are also essential for cell viability and for the maintenance of chromosome structure. Pad1 is also responsible for resistance to staurosporine, and other drugs such as cycloheximide and caffeine. 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). Belongs to the peptidase M67A family.