Immunofluorescence of U2OS and HeLa cells treated with the peptide pool (2 μg/ml) for 24 and 96 hours. Top panel: confocal microscope images of phospho-foci stained with γH2AX antibody (green) and DAPI (blue). Lower panel: percentage of γH2AX positive cells, and average number of γH2AX foci per cell as scored from 100 cells. Error bars show the standard deviation obtained from four independent experiments. Student’s test. *p < 0.05 **p < 0.01.