Karyopherin adaptor required for nuclear translocation of the proteasome; mediates interaction between nuclear import factor Srp1p and the proteasome; nuclear import of the 26S proteasome is coupled to RanGTP-initiated, ubiquitin-independent proteasomal degradation of Sts1p; Sts1p and Srp1p couple proteasomes to nascent polypeptides emerging from the ribosome for cotranslational degradation; role in ubiquitin-mediated protein degradation; contains a bipartite nuclear localization sequence