Accepts ubiquitin from the E1 complex and catalyzes its covalent attachment to other proteins (By similarity). Together with ubc-18, required for the ubiquitination of membranous organelles, and the removal of paternal mitochondria from early embryos (PubMed:31153831). S-ubiquitinyl-[E1 ubiquitin-activating enzyme]-L-cysteine + [E2 ubiquitin-conjugating enzyme]-L-cysteine = [E1 ubiquitin-activating enzyme]-L-cysteine + S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine. S-ubiquitinyl-[E1 ubiquitin-activating enzyme]-L-cysteine + [acceptor protein]-N-terminal-amino acid = [E1 ubiquitin-activating enzyme]-L-cysteine + N-terminal-ubiquitinyl-[acceptor protein]. Protein modification; protein ubiquitination. RNAi-mediated knockdown does not alter the ubiquitination of membranous organelles (MOs) or the number of MOs (PubMed:31153831). Double RNAi-mediated knockdown together with ubc-18 reduces the ubiquitination of MOs (PubMed:31153831). Double knockdown also reduces the number of lgg-1-positive autophagosome vesicles in embryos (PubMed:31153831). Belongs to the ubiquitin-conjugating enzyme family.