PIAS2-2 (PIASx-alpha) SUMOylates THRA (alpha-1 isoform) with SUMO1 at lysine-283 and lysine-389 (Liu et al. 2012). (A lysine residue corresponding to lysine-389 does not exist in the alpha-2 isoform.) SUMOylation by SUMO3 but not SUMO1 enhances induction of gene expression in response to the ligand triiodothyroxine.