Acts as an E3 ubiquitin-protein ligase for smad4. Promotes ectoderm embryonic development at the expense of other germ layers. Inhibits mesodermal differentiation. Promotes neural development of the ectoderm. Promotes smad4 alpha degradation via the ubiquitin proteasome pathway. May act as a transcriptional repressor (By similarity). 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. May interact with smad4. Expressed at the animal pole of unfertilized eggs and throughout cleavage stages in the prospective ectoderm germ layer. Expressed at the animal pole and extending up to the marginal zone at blastula stage. At the onset of gastrulation remains asymmetrically enriched in the dorsal side of the early gastrula. Its expression progressively diminishes as gastrulation proceeds (at protein level).