Fig. 4. hCdt1 is required for the loading of MCM2 onto chromatin. (A) U2OS cells were synchronized either at G1/S border with aphidicolin (5 µg/ml) for 24 hours or at G2/M transition with nocodazole (50 ng/ml) for 16 hours as indicated. The graph summarizes the number of cells showing MCM2 nuclear staining with (black bars) or without (grey bars) Triton X-100 extraction before fixation. (B) U2OS cells were treated as in Fig. 3A. The graph summarizes the percentage of cells showing MCM2 chromatin binding in the indicated conditions. Representative fields are shown in C. Original magnification x550.