The dimeric enzyme acts as an E1 ligase for SUMO1 and SUMO2. It mediates ATP-dependent activation of SUMO proteins and formation of a thioester with a conserved cysteine residue on SAE2. Protein modification; protein sumoylation. Heterodimer of SAE1A or SAE1B and SAE2. The complex binds SUMO proteins via SAE2 (By similarity). Embryonic lethal. Belongs to the ubiquitin-activating E1 family. Sequencing errors.