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 substrates (By similarity). Involved in the negative regulation of the Ras/MAPK signaling pathway in the wing by acting with the E2 enzyme Unc6 and the putative E3 ligases poe and Kcmf1 to mediate the ubiquitination and proteasomal degradation of rl/MAPK (PubMed:27552662). 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. Belongs to the UPL family. K-HECT subfamily.