EXO1 knockdown regulates the clonogenic survival, γ-H2AX locus formation and ATM accumulation in YY-8103 cells. (a) Clonogenic survival fractions of cells irradiated with a single dose of 0, 2, 4, 6 and 8 Gy X-rays. Survival curves were obtained by means of 3 standard colony formation assay. (b) γ-H2AX loci of cells irradiated with a single dose of 2 Gy. Quantitative analysis of γ-H2AX foci per cell averaged over 50 cells per data point. (c) ATM accumulation of cells irradiated with a single dose of 2 Gy revealed by western blots. Statistical significance was determined by two-tailed Student’s t test. *, P < 0.05; **, P < 0.01.