HDAC1 is SUMOylated at lysine-444 and lysine-476 with SUMO1 (Kirsh et al. 2002, David et al. 2002, Cheng et al. 2004, Citro et al. 2013). SUMOylation with SUMO1 enhances transcription repression by HDAC1 and promotes degradation of HDAC1 (Citro et al. 2013). HDAC1 can also be SUMOylated with SUMO2, which enhances stability of HDAC1 (Citro et al. 2013).