RAD51C assembles before and independently of RAD51 at sites of DNA damage. (A) HeLa cells were incubated with 2 mM HU for 17 h and then released into fresh medium. Cells were fixed 0.1 or 4 h after release and stained with anti-RAD51C (red) and anti-RAD51 antibodies (green). (B) For each of the two samples in A, at least 100 cells were examined for the presence of RAD51 or RAD51C foci. The mean and standard deviations of three independent experiments are shown. (C) CAPAN-1 (Brca2^−/tr) cells were irradiated (10 Gy), fixed 2 h after irradiation, and stained with anti-RAD51C (red) and anti-RAD51 antibodies (green). Bars, 10 µm.