| To identify the ubiquitination pathway that is linked to Nedd 4 , we demonstrated that specific E 2 enzymes , including human Ubc 4 , UbcH5B , UbcH5C , UbcH 6 and UbcH 7 , could transfer ubiquitin molecules to Nedd 4 at the active cysteine residue , whereas E6AP accepted ubiquitins from Ubc 4 , UbcH5B , UbcH5C and UbcH 7 . ^^^ |