Figure 8.

Labeling replication sites at early S-phase for two consecutive cell generations. Replication sites in synchronized mouse 3T3 fibroblasts were first labeled for 30 min with CldU (FITC secondary antibody, green sites) at the 1st G₁/S border, chased, and blocked at the 2nd G₁/S border, and then pulsed again for 30 min with IdU (Texas red secondary antibody, red sites). (A) Original image (yellow replication sites mean DNA replicated at the second G₁/S border occurs at same site as at the first G₁/S border); (B) 4× enlargement of original replication sites; (C) Protocol for labeling replication sites at the G₁/S borders for two consecutive cell generations. APC stands for aphidicolin. Bar, 5 μm.