Fig. 3. hCdt1 function is essential for DNA replication initiation. (A) Nocodazole treated, G2/M arrested U2OS cells were microinjected with anti-Cdt1 (black bars) or anti-Cdt1 antibodies neutralized with antigen peptide (dashed bars). Microinjected cells (white arrows) also express GFP. 20 hours after nocodazole release in the presence of BrdU, cells were fixed and scored for BrdU incorporation. The graphs summarize the number of BrdU-positive cells in each sample. The number of scored cells is indicated. Original magnification x63. (B) HU-treated, S-phase arrested cells were injected as in A. Cells were released from HU into fresh medium for 20 hours. BrdU was present for the first 7 hours after HU release. Original magnification x630.

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