The UBX (Ubiquitin regulatory X) domain is an 80 amino acid motif that is usually present on the carboxy-terminus of certain eukaryotic proteins. UBX domain-containing proteins (UBXD), such as FAF1, p33ING1 and D8S2298E, are typically involved in ubiquitin-related processes. UBXD proteins also constitute the largest family of VCP cofactors and are generally involved in substrate recruitment to VCP, as well as regulation of its activity. UBXD2B (UBX domain-containing protein 2B), also known as NSFL1 cofactor p37 and p97 cofactor p37, is a 331 amino acid protein that contains one UBX domain and one SEP domain. UBXN2B is required for ER and Golgi biogenesis and also plays a role in their maintenance during interphase, as well as their reassembly at the end of mitosis. Through interaction with VCP, UBXN2B forms a complex that has membrane fusion activity.