Top. Representative images of nuclei (DAPI stained, blue) with RAD51 (green) foci in HeLa cells transfected with the indicated siRNAs and treated with HU or MMC, as indicated in panel A. The scale bar represents 10 μm. Bottom. Histograms presenting the percentage of RAD51 foci-positive cells as evaluated in the different conditions of above. Data represent the means+/-S.E.M. and were analyzed by unpaired t-test. siSMC6 vs siLacZ: n=3, NT, MMC or HU p=n.s.; siFANCD2 vs siLacZ: n=4, NT p=n.s., MMC p=0.0003, HU p=0.0479; siSMC6+siFANCD2 vs siLacZ: n=3, NT p=n.s., MMC p=0.0439, HU p=0.0458. 