Has E3 ubiquitin ligase activity, promoting ubiquitination and degradation of target proteins (PubMed:11823428, PubMed:22159038, PubMed:26575292). Involved in activation of the JAK/STAT pathway (PubMed:11823428, PubMed:22159038). Catalyzes ubiquitination of methylated RBM15 (PubMed:26575292). Plays a role in quality control of translation of mitochondrial outer membrane-localized mRNA (PubMed:29861391). As part of the PINK1-regulated signaling, upon mitochondria damage, ubiquitinates ABCE1 and thereby recruits autophagy receptors to the mitochondrial outer membrane to initiate mitophagy (PubMed:29861391). 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. Interacts with CNOT1 via its C-terminus but does not stably associate with the CCR4-NOT complex (PubMed:11823428). Interacts (via RING domain) with UBE2D2 (PubMed:15001359). Interacts with ABCE1, PINK1 and PELO (PubMed:29861391). Autoubiquitinated. Sequencing errors.