Has a role in de-ubiquitination. In conjunction with UBP3, cleaves ubiquitin, leading to the subsequent mono-ubiquitination of sec23. Heterotetramer with UBP3; contains two molecules of BRE5 and two molecules of UBP3 (PubMed:12778054, PubMed:17632125). Forms a complex composed of CDC48, DOA1, deubiquitinase UBP3 and probably BRE5 (PubMed:20508643). Within the complex, interacts (via C-terminus) with CDC48; the interaction is direct and UBP3-independent (PubMed:20508643). Present with 11700 molecules/cell in log phase SD medium.