Substrate specificity imparted by E3–substrate interactions are thought to be particularly important for directing conjugation to non-consensus Lys residues. Substrates modified by SUMO can contact SUMO-binding proteins through their SUMO-interacting motifs (SIMs) (step 8). Deconjugation is performed by Ulp and SENP proteases and free SUMO may be recycled for another round of conjugation (step 9).