All SUMO isoforms are translated with additional C-terminal residues that have to be removed to generate the active protein. Pro-SUMO-3 (103amino acids) is the inactive precursor of SUMO-3 (92 amino acids) and is processed at the C-terminus by SUMO-3 specific proteases (SENPs). The resulting SUMO-3 protein has the conserved C-terminal Gly-Gly residues that function in activation and conjugation reactions. This protein can be used as a negative control in SUMOylation reactions or as a substrate for SENPs. NCBI Accession # NM_006936.