Versatile protein that might stabilize multiple protein complexes involved in diverse pathways. Subunit of the 26S proteasome which plays a role in ubiquitin-dependent proteolysis (PubMed:16149916). Acts as a ubiquitin receptor of the 26S proteasome, by interacting with ubiquitin chains linked by 'Lys-63' and 'Lys-48' (PubMed:25306921). Involved in nuclear export of specific sets of mRNAs (PubMed:18023413). Links the mRNA adapter mlo3 to rae1 for targeting mRNA-protein complex to the proteins of the nucleoporin complex (NPC) (PubMed:15990877). Involved in recombinational repair of DNA. Plays a critical role in linking repair and checkpoint factors to damaged DNA sites by specifically recruiting rad24 and cdc25 to the DSBs (PubMed:20231270). Interacts with mlo3, rae1, nup98/nup189 and nup146 (PubMed:15990877). Interacts with rad24 (PubMed:20231270). Interacts (via UBSs) with ubiquitin (ubi3/ubi5) (PubMed:25306921). Two unstructured ubiquitin-binding sites (UBSs) mediate interaction with ubiquitin. UBS-I is the strong and UBS-II the weak binding site. Belongs to the DSS1/SEM1 family.