Heterodimeric E1-activating enzyme initiating the SUMOylation cascade, essential for protein modification and genome stability. Recombinant full length human SAE1 (UBLE1A) and human UBA2 (SAE2) were co-expressed by baculovirus in Sf9 insect cells using an N-terminal His tag on SAE1 and GST tag on UBA2. Molecular weight ~39 kDa (SAE1); ~115 kDa (UBA2). Supplied as sterile 50 mM Tris-HCl, pH 7.5, 50-300mM NaCl, 10mM glutathione, 0.1mM EDTA, 0.25-1.0mM DTT, 0-0.1mM PMSF, 10-25% glycerol. Store product at –70°C. For optimal storage, aliquot target into smaller quantities. Avoid repeated handling and multiple freeze/thaw cycles.