E3 ubiquitin-protein ligase. 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 (via PDZ domain 1) with kidins220b (via PDZ-binding motif). Localizes to the postsynaptic region of neuromuscular junctions. Detected in the presumptive hindbrain and notochord from the 3-somite stage onwards (PubMed:22252497). Expression in notochord becomes restricted to the posterior as development proceeds (PubMed:22252497, PubMed:22609016). Shows particularly strong expression at the hindbrain-rhombomere 1 boundary during the 12-18 somite stages (PubMed:22252497, PubMed:22609016). Expressed in ventral spinal cord neurons and ventral somite cells at 24 hours post-fertilization (hpf) (PubMed:22252497). Becomes restricted to trunk-tail motor neurons at 32 hpf (PubMed:22252497, PubMed:22609016). Detected in eye primordia from the 10-somite stage onwards (PubMed:22252497). At 24 hpf, expression in eye is found in the ventral retina and optic stalk, and also weakly in dorsal retina (PubMed:22252497). Expressed in the eye choroid fissure and ganglion cells at 32 hpf (PubMed:22252497, PubMed:22609016). Also found in thalamus, posterior tuberculum, head mesenchyme, pectoral fins and pronephric duct at 32 hpf (PubMed:22252497). The RING-type zinc finger domain is required for E3 ligase activity.