E3 ubiquitin-protein ligase which accepts ubiquitin from an E2 ubiquitin-conjugating enzyme in the form of a thioester and then directly transfers the ubiquitin to targeted substrate (PubMed:32339205). Required for regulation of cell proliferation in imaginal disks and germ cells. Acts as a negative regulator of hh, ci and dpp expression in the anterior of the eye disk (PubMed:12421709, PubMed:7958417). Catalyzes 'Lys-63'-linked polyubiquitination of akirin, thereby activating the immune deficiency pathway (Imd) (PubMed:32339205). 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. Expressed at all stages of development, with high levels at the embryonic and pupal stages (at protein level). Ectopic expression of hh and dpp, resulting in non autonomous overgrowth of the disc and premature photoreceptor differentiation that propagates into the surrounding tissue. A cysteine residue is required for ubiquitin-thioester formation.