Fig. 4. Activation of DNA damage response pathways. EJ30 cells were grown on coverslips and were either used as control (untreated) or treated with 500 µM mimosine for 24 hours. After fixation, the cells were stained with antibodies against (A) -H2AX (green) and RPA (red), (B) RPA34 (green) and ATR (red) and (C) -H2AX (green) and phosphorylated CHK1-S317-P (red). Representative nuclei are shown in A and B. (C) To illustrate the correlation between the intensity of -H2AX staining and the level of CHK1-P, a low magnification field of nuclei is shown. Merged RGB images are shown in the right hand panels.