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. Down-regulates Dpp signaling after gastrulation by promoting MAD ubiquitination and subsequent degradation. 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 phosphorylated MAD. Uniformly expressed at blastoderm stage. Weakly but broadly expressed at later stages of embryogenesis. Flies exhibit lethal defects in hindgut morphogenesis.