fluorescence signal at RPA foci per cell (C) of the indicated mutants. ssDNA repair efficiency was determined from the maximal and final percentages of cells with RPA foci during the time course (B, right panel). Cells were synchronized in G1, irradiated with 20 J/m2 and released into S phase for different times. The percentage of cells with foci at each point was normalized to the highest value of the wild type, taken as 100 (B, middle panel). Cell cycle progression was determined by cell sorting (B, left panel). Counting and quantification were done with the MetaMorph software. The mean and SEM of 4 independent experiments are shown. Statistically significant differences according to a paired two-tailed Student's t-test are shown, where two and three asterisks represent p-values <0.01 and <0.001, respectively. 