Acts as an E4 ubiquitin ligase mediating the assembly of polyubiquitin chains on substrates ubiquitinated by another E3 ubiquitin ligase (PubMed:27669035). The elongation of preexisting ubiquitin chains preferentially targets ubiquitin 'Lys-29' and 'Lys-48' residues (PubMed:27669035). Also functions as an E3 ligase in conjunction with specific E1 and E2 ligases (PubMed:15294159, PubMed:27669035, PubMed:29396393). Probably by regulating protein ubiquitination at DNA damage repair sites, coordinates DNA double-strand-break repair and apoptosis in the germline (PubMed:27669035). Required for germline apoptosis in response to DNA damage downstream of cep-1 (PubMed:27669035). Involved in the resolution of DNA-repair sites by promoting the release of rad-51 from DNA damage foci (PubMed:27669035). In association with protein-ligase chn-1, acts as an E3/E4 ligase to poly-ubiquitinate lysine residues in the UCS domain of myosin chaperone unc-45 (PubMed:15294159, PubMed:29396393). By targeting myosin chaperone unc-45 for proteasomal degradation, regulates myosin assembly in body wall muscles in association with cdc-48.1 and chn-1 (PubMed:15294159, PubMed:17369820). However, in a contrasting study, acts as an E3 ligase, independently of chn-1, to poly-ubiquitinate unc-45 without promoting unc-45 proteasomal degradation (PubMed:29396393). Instead, uses unc-45 as an adapter protein to recruit and poly-ubiquitinate unfolded myosin heavy chain B unc-54 (PubMed:29396393). S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. Protein modification; protein ubiquitination. Forms a complex composed of deubiquitinating enzyme atx-3, E4 ubiquitin-protein ligase ufd-2 and cdc-48.1; within the complex interacts with atx-3 and cdc-48.1 (via DDDLYN motif) (PubMed:21317884, PubMed:27669035). Forms a complex composed of cdc-48.1, myosin chaperone unc-45, ubiquitin-protein ligases ufd-2 and chn-1; the complex targets myosin chaperone unc-45 for proteasomal degradation; within the complex interacts with cdc-48.1 (via DDDLYN motif), chn-1 and unc-45 (PubMed:17369820, PubMed:15294159, PubMed:27669035). Forms a complex composed of unc-45 and myosin heavy chain B unc-54; the complex targets unfolded unc-54 for proteasomal degradation; within the complex interacts with unc-45 (via TPR domain) and unc-54 (PubMed:29396393). Interacts with cdc-48.2 (via DDDLYN motif) (PubMed:21317884, PubMed:17369820). Localizes to germline syncytium. In the late pachytene, accumulates at the nuclear periphery forming a ring. Following ionizing radiation-mediated DNA damage, localizes to foci within nucleoli where it colocalizes with cdc-48.1 and/or cdc-48.2, atx-3, proteasome alpha subunit and ubiquitinated proteins. Localization to foci is ubiquitin-dependent and regulated by E3 ligase hecd-1 and deubiquitinating enzyme atx-3. ufd-2 foci are formed following the initiation of homologous recombination (HR) and persist until HR is completed. ufd-2 foci are also formed upon cep-1 activation. Expressed in the germline (at protein level). Expressed in young adults but not in larvae (PubMed:17369820). Expressed in pharyngeal muscles and in body wall muscles in L2 and L4 larvae, respectively (PubMed:15294159). The U-box domain is required for the ubiquitin protein ligase activity. Number of germline apoptotic corpses is decreased in response to ionizing radiation-mediated DNA damage but not following UV-induced DNA damage (PubMed:27669035). Delay in the dissociation of rad-51 from DNA damage foci (PubMed:27669035). In a hecd-1 (tm2371) mutant background, the decrease in the number of germline apoptotic corpses is more severe (PubMed:27669035). In an atx-3 (gk193) mutant background, prevents the increase in the number of germline apoptotic corpses (PubMed:27669035). RNAi-mediated knockdown in an unc-45 (m94) mutant background restores motility (PubMed:17369820). Belongs to the ubiquitin conjugation factor E4 family. The role of chn-1 in ufd-2-mediated unc-45 ubiquitination is controversial. While two studies showed that unc-45 ubiquitination by ufd-2 requires ubiquitin-protein ligase chn-1, one study showed that ufd-2 ubiquitinates unc-45 independently of chn-1.