Accepts the ubiquitin-like protein smo-1 from the aos-1-uba-2 E1 complex and catalyzes its covalent attachment to other proteins with the help of an E3 ligase such as gei-17. Required to sumoylate the ETS transcription factor lin-1, Polycomb protein sop-2, and intermediate filament proteins, such as ifb-1 (PubMed:15107848, PubMed:15689373, PubMed:24933177). Required for embryonic development, fertility, vulval morphogenesis, inhibition of vulval cell fates, lifespan, and neuromuscular activity (PubMed:24933177). Protein modification; protein sumoylation. Interacts with brd-1 and rad-51 (PubMed:14711411). Interacts with smo-1 and sop-2 (Ref.1, PubMed:15107848). Interacts with bet-1 (via BROMO domain 2) (PubMed:24349540). Interacts with isoforms 1 and 2 of X-box-binding protein xbp-1. Ubiquitously expressed throughout development (at protein level) (PubMed:24933177). Expressed in early embryos in utero, in the pharynx and body-wall muscles during larval stages, becoming prominent in coelomocytes and the male tail in young adults (PubMed:24933177). RNAi-mediated knockdown results in sterility, embryonic lethality and sensitivity to radiation (PubMed:14711411, PubMed:25873636). RNAi-mediated knockdown causes a number of defects during the first embryonic mitotic division including loss of smo-1 from metaphase chromosomes, chromosome misalignment at metaphase, diminished spindle pole separation, slow chromosome segregation, decreased distance between chromosomes afer anaphase onset and increased air-2 levels in the spindle midzone (PubMed:25475837). RNAi-mediated knockdown results in ectopic tbx-2 expression in seam cells, the gut and in the syncytial hypodermis (PubMed:25873636). Exhibits abnormal localization and structure of intermediate filament protein ifb-1, such as altered filaments and aggregates, resulting in elongation defects of embryos. Belongs to the ubiquitin-conjugating enzyme family.