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. Associates also with the TREX-2 complex that is required for transcription-coupled mRNA export, and the COP9 signalosome, which is involved in deneddylation. Part of the 26S proteasome. Associates with the nuclear pore complex (NPC)-associated TREX-2 complex and the COP9 signalosome. Interacts with CSN12 and THP3. Impairs mRNA export and transcription elongation, and induces strong transcription-associated hyperrecombination phenotypes. Present with 5590 molecules/cell in log phase SD medium. Belongs to the DSS1/SEM1 family.