(E3-independent) E2 ubiquitin-conjugating enzyme (UBE2O)

E2/E3 hybrid ubiquitin-protein ligase that shows both E2 and E3 ligase activities and mediates monoubiquitination of target proteins (PubMed:23455153, PubMed:24703950). Negatively regulates TRAF6-mediated NF-kappa-B activation independently of its E2 activity (PubMed:23381138).

Acts as a positive regulator of BMP7 signaling by mediating monoubiquitination of SMAD6, thereby regulating adipogenesis (PubMed:23455153). Mediates monoubiquitination at several sites of the nuclear localization signal (NLS) of BAP1, leading to cytoplasmic retention of BAP1.