SUMO-Conjugating Enzyme UBC9 (UBC9) belongs to the ubiquitin-conjugating enzyme family. UBC9 is homologous to ubiquitin-conjugating enzymes (E2s). However, instead of conjugating ubiquitin, UBC9 conjugates a ubiquitin homologue, Small Ubiquitin-Like Modifier 1 (SUMO-1). The conjugation of ubiquitin requires the activities of ubiquitin-activating (E1) and conjugating (E2) enzymes. It is suggested that UBC9 might play a role in DNA repair and perhaps even in aging.