Essential component of the ubiquitin-dependent proteolytic pathway which degrades ubiquitin fusion proteins. The ternary complex containing UFD1, VCP and NPLOC4 binds ubiquitinated proteins and is necessary for the export of misfolded proteins from the ER to the cytoplasm, where they are degraded by the proteasome. The NPLOC4-UFD1-VCP complex regulates spindle disassembly at the end of mitosis and is necessary for the formation of a closed nuclear envelope. It may be involved in the development of some ectoderm-derived structures (By similarity). Acts as a negative regulator of type I interferon production via the complex formed with VCP and NPLOC4, which binds to DDX58/RIG-I and recruits RNF125 to promote ubiquitination and degradation of DDX58/RIG-I (PubMed:26471729). Protein degradation; proteasomal ubiquitin-dependent pathway. Heterodimer with NPLOC4, this heterodimer binds VCP and inhibits Golgi membrane fusion (PubMed:11574150, PubMed:26471729). Interacts with USP13 (PubMed:21571647). Interacts with ZFAND2B; probably through VCP (PubMed:24160817). Found in adult heart, skeletal muscle and pancreas, and in fetal liver and kidney. Major isoform. Belongs to the UFD1 family.