The SUMO1 precursor has 4 extra residues at the C-terminus which can be removed endoproteolytically by either SENP1, SENP2, or SENP5 (Zheng and Au, 2005, Mikolajczyk et al. 2007). The order of processing activity is: SENP1 greater than SENP2 greater than SENP5 (Mikolajczyk et al. 2007). Both SENP1 and SENP2 shuttle between the nucleus and cytoplasmic and both are predominantly nucleoplasmic (Bailey and O'Hare 2004, Kim et al. 2005, Zhang et al. 2002, Hang and Dasso 2002, Itahana et al. 2006).