Accepts ubiquitin from the E1 complex and catalyzes its covalent attachment to other proteins ( ). E2 ubiquitin conjugating enzyme that transfers ubiquitin to MAEA, a core component of the CTLH E3 ubiquitin-protein ligase complex . In vitro catalyzes 'Lys-11'- and 'Lys-48'-linked polyubiquitination . Capable, in vitro, to ubiquitinate histone H2A .