Co-repressor activity of scaffold attachment factor B1 requires sumoylation

► SAFB1 is sumoylated to two lysine residues K231 and K294. ► SAFB1 sumoylation is regulated by PIAS1 and SENP1. ► Sumoylation of SAFB1 regulates its transcriptional repressor activity. ► Mutation of sumoylation sites leads to decreased SAFB1 binding to HDAC3.