Substrate-recruiting cofactor of the CDC48-NPL4-UFD1 segregase (PubMed:31249135). Assists CDC48 in the dislocation of misfolded, polyubiquitinated ERAD substrates that are subsequently delivered to the proteasome for degradation (PubMed:11739805, PubMed:11740563, PubMed:11847109). Involved in the import of nuclear-targeted proteins into the nucleus and the export of poly(A) RNA out of the nucleus (PubMed:8930904, PubMed:11733065). Required for the proteasome-dependent processing/activation of MGA2 and SPT23 transcription factors leading to the subsequent expression of OLE1 (PubMed:11733065). Regulates ubiquitin-mediated mitochondria protein degradation (PubMed:31249135). Involved in spindle disassembly probably by promoting the degradation of spindle assemby factors ASE1 and CDC5 at the end of mitosis (PubMed:14636562). Component of the heterotrimeric CDC48-NPL4-UFD1 ATPase complex (PubMed:16873066). The CDC48-NPL4-UFD1 ATPase complex interacts with the HRD1 ubiquitin ligase complex composed of the E3 ligase HRD1, its cofactors HRD3, USA1 and DER1, substrate recruiting factor YOS9 and CDC48-binding protein UBX2 (PubMed:16873066). Interaction between the complexes is mediated by interaction between CDC48-NPL4-UFD1 complex member CDC48 and HRD1 complex member UBX2 (PubMed:16873066). Forms a complex composed of CDC48, NPL4, UFD1, DOA1, SHP1 and deubiquitinase OTU1 (PubMed:16427015). Interacts with CDC48, UFD1 and VMS1 (PubMed:11598205, PubMed:11733065, PubMed:11739805, PubMed:21070972, PubMed:31249135). Localizes mainly at the nuclear periphery and the endoplasmic reticulum membrane. Present with 1050 molecules/cell in log phase SD medium. Belongs to the NPL4 family.