Fig. 7. Shape of the HSR domain in the late G2 phase nucleus. The clone-22 cells were pulse-labeled with IdU, chased for 100 minutes, pulse-labeled with CldU, further chased, and harvested 4 hours after the IdU-labeling. The incorporated IdU or CldU was detected simultaneously with the HSR, as in Fig. 4. Representative images of the interphase nuclei are shown whose nuclei should be at the late G2 phase at the time of harvest, because the late-replicating HSR was labeled with CldU (A) or IdU (B). The HSR detected by FISH is (A) ring-shaped or in an (B) extended pair of spirals. Arrows indicate HSR (A',B') labeled with CldU (A''') or IdU (B'').