SUMO1 is a protein that belongs to the SUMO （small ubiquitin-like modifier） protein family. SUMO1 functions in a manner similar to ubiquitin in that it is bound to target proteins as part of a post-translational modification system. Still， unlike ubiquitin which targets proteins for degradation， SUMO1 is involved in a variety of cellular processes， for example nuclear transport， transcriptional regulation， apoptosis， and protein stability. SUMO1 is not active until the last four amino acids of the carboxy-terminus are cleaved off.
