Fig. 3. Cell-cycle dependence of -H2AX, DNA-PK_cs and Rad51 foci after irradiation with 960 kJ/m². (A) Frequencies of -H2AX, DNA-PK_cs and Rad51 foci in cell-cycle-synchronised cells. The Rad51 foci are mainly formed in G₂ phase, whereas there are only a small number of cells with Rad51 foci in G₁. By contrast, the DNA-PK_cs and -H2AX foci are not related to the cell-cycle stage. (B-D) Sample micrographs of Rad51 foci, DNA-PK_cs foci and H2AX foci in synchronised cells. The Rad51 foci are prevalent in S and G₂ phases, whereas the -H2AX (right) and DNA-PK_cs (middle) are not. Each experiment has been independently repeated and 2x200 cells were scored. (E) Flow-cytometric analysis of cell-cycle position after propidium iodide staining of total DNA.