Figure 3.

The fluorescence intensities of replication foci. Cells synchronized at the beginning of S phase were grown for 20 min in medium containing BrdU, and then 20 h or 5 d in medium. Sites of BrdU incorporation were indirectly immunolabeled with FITC and images recorded using a CCD camera. A shows a typical cell in the first G1 phase after labeling and (B and C) two cells that indicate the range of labeling 5 d later. Raw images were collected, noise removed, and the intensities of individual foci were determined (D). 621 sites (D, open bars) chosen from random areas of six cells like A, and 430 sites (D, closed bars) all foci from seven cells like B and C were measured. Bar, 2.5 μm.