Fig. 1

The SUMO cycle. SUMO is produced as a precursor which is processed by SENP to expose the C terminal diglycine residues (MATURATION). SUMO is then activated by heterodimer E1 enzyme in an ATP dependent manner (ACTIVATION). SUMO is then transferred to the SUMO E2 conjugating enzyme, Ubc9 (CONJUGATION). Further, SUMO is attached to the substrate either in the presence of E3 (with or without substrate binding) or directly by Ubc9 (LIGATION). Depending on the substrate and function, more than one SUMO molecules can be bound (POLYSUMOYLATION). SUMOylation is reversed by SENPs, releasing the SUMO molecule(s) for the next cycle