A: Diamide is inducing the SUMO E1~E2 disulfide but not ATM phosphorylation. U2OS stable cell populations were depleted from endogenous Ubc9 by siRNA for 72 h before addition of 500 µM diamide or 500 µM H2O2. Cells were subsequently washed in PBS with 20 mM NEM and lysed in Laemmli buffer. The lysates were resolved by SDS-PAGE. 