A. Conjugation and deconjugation of SUMO (shown in 3D structure rendering) are outlined. SUMO forms a thioester bond with the heterodimeric E1 (Aos1/Uba2) in an ATP-dependent manner. SUMO is then transferred to the E2 (Ubc9), again forming a thioester bond. SUMO is conjugated to the lysine residue (K) on the substrate with the help of SUMO E3. Only a single SUMO conjugation is shown, but multiple SUMOs or SUMO chains can also be found on substrates. SUMO proteases cleave SUMO from the substrate.
B. A brief summary of major effects of sumoylation on nuclear structure and functions. Nuclear domains and chromosomal regions enriched with SUMO are indicated by . Sumoylation also regulates transcription and DNA lesion repair as indicated. Arrow: positive effects; lines: negative effects. Arrows pointing to the nuclear pore complex (NPC) and nuclear envelope indicate SUMO-mediated DNA movement toward these locations.