Marked for death

SUMOylation of PML-RaR alpha oncoprotein has been linked to its arsenic-induced degradation and the therapeutic response in acute promyelocytic leukaemia. Two groups identify PML as an in vivo target of the RING finger ubiquitin E3 ligase RNF4, which specifically binds polysUMOylated PML and is essential for the arsenic-induced catabolism of both PML and PML -RaR alpha.