Ubiquitin-like modifier-activating enzyme 6 (UBA6)

Activates ubiquitin by first adenylating its C-terminal glycine residue with ATP, and thereafter linking this residue to the side chain of a cysteine residue in E1, yielding a ubiquitin- E1 thioester and free AMP. Particular for ubiquitin, doesn't activate ubiquitin-like peptides.

Differs from UBE1 in its specificity for substrate E2 charging. Doesn't bill cell cycle E2s, such as CDC34.