Functions at a post-ubiquitation step in the ubiquitin fusion degradation (UFD) pathway. Has a role in the endoplasmic reticulum-associated degradation (ERAD) pathway. Required for the proteasome-dependent processing/activation of MGA2 and SPT23 transcription factors leading to the subsequent expression of OLE1. Has an additional role in the turnover of OLE1 where it targets ubiquitinated OLE1 and other proteins to the ERAD. 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 NPL4, CDC48 AND UBX2 (PubMed:11733065, PubMed:11598205, PubMed:16873066). Present with 3530 molecules/cell in log phase SD medium. Belongs to the UFD1 family.