Fig. 2. The replication capacity of CHOC 400 G1-phase nuclei is independent of the presence of XMcm3 in Xenopus egg extracts. Synchronized CHOC400 cells were permeabilized with 80 µg/ml (A,B) or 400 µg/ml (C,D) digitonin to prepare cells with intact or permeabilized nuclei, respectively. Permeabilized cells were introduced in mock-depleted (A,C) or XMcm3-depleted (B,D) Xenopus egg extracts supplemented with [-³²P]dATP. Aliquots were removed at the indicated times and the percentage of input DNA replicated was determined by acid precipitation as described (Dimitrova and Gilbert, 1998). Similar results were obtained in three independent experiments. Filled squares represent metaphase cells; diamonds, 1 hour; filled circles, 2 hours; triangles, 4 hours; hatched squares, 6-hour G1-phase nuclei; and hatched circles, G1/S-phase nuclei.