NCIt definition : An ATP-dependent aminoacyltransferase that catalyzes the third step in the ubiquitination
reaction via the transfer of ubiquitin from an E2 ubiquitin-conjugating enzyme to
lysine residues found in the final substrate protein.;
NCIt note : The IUBMB has recategorized E3 ubiquitin-protein ligases as transferases (EC 2); specifically
aminoacyltransferases (EC 2.3.2.-). There are at several categories of E3 enzymes
based on the structure of the active site including: HECT-type (EC 2.3.2.26), RING-type
(EC 2.3.2.27), RING-type (cysteine targeting) (EC 2.3.2.36), RBR-type (EC 2.3.2.31)
and RCR-type (EC 2.3.2.33).;