Figure 3.

Three replication patterns visualized by BrdU immuno-detection during the S phase. The HeLa cells were labeled with BrdU for 10 min, fixed (2% formaldehyde, 10 min), permeabilized (0.2% Triton X-100, 10 min), and treated with 4N HCl (20 min). The incorporated BrdU was visualized using anti-BrdU antibody and Cy3 labeled anti-mouse antibody. Type I—large number of small replication sites characteristic for early S phase; type II—replication sites concentrated at the periphery of the nucleus and nucleoli (mid S phase); type III—large replication sites over heterochromatin (late S phase).