Sumo3 Conjugation Kit is designed for assaying the conjugation of Sumo3 to protein substrates in vitro. In a protein sumoylation reaction, a Sumo protein is first activated by the Sumo activating enzyme SAE1/SAE2 (E1) in an ATP hydrolysis-dependent manner; activated Sumo is then transferred to the Sumo conjugating enzyme Ube2I (E2) by formation of a thiolester bond with the catalytic cysteine residue of Ube2I; Sumo-charged Ube2I can mediate protein sumoylation in the presence of an appropriate Sumo ligase (E3).