Functions at a post-ubiquitination step in the ubiquitin fusion degradation (UFD) pathway (By similarity). In association with npl-4.1 and/or npl-4.2 and ATPase cdc-48.1 and/or cdc-48.2, involved in the cytoplasmic elimination of misfolded proteins exported from the ER (PubMed:16647269, PubMed:22768338). This pathway, known as ERAD, prevents the activation of the unfolded protein response (UPR) caused by the accumulation of misfolded proteins in the ER (PubMed:16647269, PubMed:22768338). During S phase and in association with npl-4.1 and/or npl-4.2, cdc-48.1 and/or cdc-48.2 and ubxn-3, ensures the degradation of DNA licensing factor cdt-1 after the initiation of DNA replication and thus the disassembly of the DNA replication CMG helicase complex by promoting the dissociation from chromatin of several of its components including cdc-45 and sld-5 (PubMed:18728180, PubMed:21981920, PubMed:26842564). Regulates ubxn-3 nuclear localization during S phase (PubMed:26842564). Forms a complex composed of ubxn-3, ufd-1, npl-4.1 and cdc-48.1; within the complex interacts with cdc-48.1 (PubMed:20977550, PubMed:16647269). Interacts with cdc-48.2 (PubMed:16647269). Interacts with npl-4.1 and/or npl-4.2 (PubMed:16647269). Localizes to the cytoplasm during mitosis. Nuclear localization upon nuclear membrane re-assembly is cdc-48-dependent. RNAi-mediated knockdown causes embryonic lethality (PubMed:16647269, PubMed:18728180). In embryos, DNA replication is partially impaired causing a delay in S phase progression in P0, AB and P1 cells; simultaneous RNAi-mediated knockdown of DNA replication checkpoint kinases chk-1 or atl-1 suppresses the delay in S phase (PubMed:18728180). Prevents DNA replication licensing factor cdt-1 down-regulation and causes cdt-1 accumulation on mitotic chromosomes (PubMed:21981920). Impairs dissociation from the chromatin of components of the DNA replication machinery, including cdc-45 and GINS complex component sld-5, resulting in their persistent association with chromatin throughout embryonic mitosis (PubMed:21981920, PubMed:26842564, PubMed:18728180). Abnormal ubxn-3 localization into punctate structures in the nucleus (PubMed:26842564). Reduces npl-4 expression in embryos (PubMed:21981920, PubMed:26842564). RNAi-mediated knockdown in adults causes defects in germline development, induces the unfolded protein response, and causes the accumulation of misfolded protein cpl-1 in the ER (PubMed:16647269, PubMed:20977550, PubMed:22768338). Belongs to the UFD1 family.