PIAS4 SUMOylates PARP1 at lysine-203 and lysine-486 with SUMO1 (Martin et al. 2009, Matafora et al. 2009, Messner et al. 2009, Zilio et al. 2013, Impens et al. 2014). SUMOylation abrogates acetylation of PARP1 by p300 (Messner et al. 2009). PARP1 reciprocally poly(ADP-ribose)ylates PIAS4 (Martin et al. 2009). PARP1 is SUMOylated in response to heat shock and SUMOylation is required for full activation of the HSP70.1 promoter (Martin et al 2009).