In both mESCs and APL mice, stable expression of a His10-SUMO2 mutant defective for chain formation (SUMO2K/R)27 blocked arsenic-increased global SUMO2 conjugation (Fig. 1e and Supplementary Fig. 1h), while critically, arsenic-induced PML multi-sumoylation was preserved. The gene discussed is SUMO2; the disease is acute promyelocytic leukemia.