Regulation of SUMOylation through target modification. Distinct post-translational modifications of the target protein can affect its sumoylation. A) Competition with other lysine-directed modifications such as ubiquitinylation of acetylation abolishes sumoylation. B) Phosphorylation can act both as a positive and a negative regulator of sumoylation. Enhanced sumoylation has been observed, e.g., when the phosphorylated residue is part of an extended SUMO acceptor site, the PDSM (Phosphorylation Dependant SUMO Motif; with the sequence motif ΨKxExxSP ).