(C) Damaged bases repair are suppressed in U2OS cells expressing the E141A mutant (E141A). U2OS cells (WT) and U2OS H2AX knockout cells reconstituted with wild type H2AX (H2AX KO+WT), or the E141A mutant H2AX (E141A) were treated with H2O2 (2 mM in PBS, 5 minutes) or MMS (1 mM in medium, 30 minutes) and harvested at the indicated recovery time points. Then FPG-modified comet assay was performed. NT: no treatment. Representative comet tails were shown. The olive tail moments (OTM) were summarized from at least 50 cells in each experiment. Values are mean ± SD of three assays. 