SUMO1, 2, and 3 are initially expressed as propeptides containing extra residues at the C-terminus. (SUMO1 has 4 residues, SUMO2 has 2 residues, and SUMO3 has 11 residues,) SENP1, 2, and 5 are endoproteases that process the precursors to produce the mature peptides (reviewed in Wang and Dasso 2009, Wilkinson and Henley 2010, Hannoun et al. 2010, Gareau and Lima 2010). SENP1 processes SUMO1 with greater efficiency than SUMO2 or SUMO3. SENP2 and SENP5 process SUMO2 with greater efficiency than SUMO1 or SUMO3 (Gong and Yeh 2006, Mikolajczyk et al. 2007). SENP1 shuttles between the cytosol and nuceoplasm and is predominantly nuclear (Bailey and O'hare 2004, Kim et al. 2005). SENP2 also shuttles (Itahana et al. 2006) and is mainly located on nucleoplasmic filaments of the nuclear pore complex (Hang and Dasso 2002, Zhang et al. 2002). SENP5 is located mostly in the nucleolus (Di Bacco et al. 2006, Gong and Yeh 2006).