Involved in protein ubiquitination, but has no ubiquitin ligase activity on its own (PubMed:15530417). The uev-1-ubc-13 heterodimer catalyzes the synthesis of non-canonical poly-ubiquitin chains that are linked through Lys-63 (PubMed:15530417, PubMed:24595290). Involved in sorting Lys-63-linked polyubiquitinated maternal membrane proteins for degradation by targeting to multivesicular bodies (PubMed:24595290). Required for glr-1-containing glutamate receptor trafficking in neurons (PubMed:21179194). May have a role in synaptic transmission at motorneurons (PubMed:21179194). May be involved in the ubiquitination and growth of intracellular polyglutamine protein aggregates (PubMed:17663792, PubMed:22494772). Heterodimer with ubc-13. Expressed in the pharynx, body wall muscle cells, vulval epithelia, distal tip cell, intestine, tail, head neurons and ventral cord motorneurons. Expressed from embryo to adulthood. Temperature sensitive with partial embryonic lethality at 25 degrees Celsius (PubMed:24595290). Inhibited degradation of maternal membrane proteins, cav-1, chs-1 and rme-2, and ubiquitination of cav-1 with accumulation of these proteins on the maternal plasma membrane and endosome-like vesicles in later-stage embryos (PubMed:24595290). Locomotion defect with animals displaying increased body flexing (PubMed:21179194). Mis-localized glr-1-containing glutamate receptor with increased glr-1 accumulation in the ventral nerve cord (PubMed:21179194). Reduced and irregular snb-1 accumulation at neuromuscular junctions (PubMed:21179194). RNAi-mediated knockdown prevents localization of ubiquitin and proteasomes to polyglutamine protein aggregates (PubMed:17663792). Reduced size of polyglutamine protein aggregates (PubMed:17663792). Inhibited degradation of the maternal membrane protein, cav-1 in embryos (PubMed:24595290). Belongs to the ubiquitin-conjugating enzyme family. Has no ubiquitin ligase activity on its own; may require ubiquitin-conjugating enzyme, ubc-13.