(C) The E141A mutation abolishes the ADP-ribosylation of H2AX. Empty vector (EV), wild type (WT) or the E141A mutant (E141A) of H2AX was expressed in U2OS H2AX knockout cells that were treated with H2O2. ADP-ribosylated proteins were IPed with anti-ADPR antibody. ADP-ribosylated H2AX was examined by Western blotting using anti-H2AX antibody. 