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 an ubiquitin-E1 thioester and free AMP. UBA6 is specific for ubiquitin and does not activate ubiquitin-like peptides. UBA6 differs from UBE1 in its specificity for substrate E2 charging. UBA6 does not charge cell cycle E2s, such as CDC34. UBE6 is essential for embryonic development and required for UBD/FAT10 conjugation [taken from the Universal Protein Resource (UniProt) www.uniprot.org/uniprot/A0AVT1].