Ubiquitin is an abundant, highly conserved protein found in all eukaryotic cells either free or covalently attached to cellular proteins. The primary function of ubiquitin in mammalian systems is to clear abnormal, foreign and improperly folded proteins by targeting them for proteosome degradation. UBA3 (ubiquitin-like modifier activating enzyme 3), also known as NEDD8-activating enzyme E1 catalytic subunit or UBE1C (ubiquitin-activating enzyme E1C), is a 463 amino acid protein belonging to the ubiquitin-activating E1 family and UBA3 subfamily. Ubiquitously expressed, UBA3 acts as an activator to NEDD8, a ubiquitin-like protein, thus regulating cell division, signaling and embryogenesis. UBA3 exists as two isoforms due to alternative splicing events.