Evidence for Sequential and Increasing Activation of Replication Origins along Replication Timing Gradients in the Human Genome
Figure 2
The global rate of DNA replication increases during S phase in HeLa cells.
(A) Histogram of replication timing values (TR50, hours) in the whole genome. (B) Histogram of global fork densities in S1, S2, S3 and S4 as determined by DNA combing. (C) Flow cytometry profile of cells pulsed labeled with 25 µM IdU/CldU for 20/20 min. IdU/CldU was stained with fluorescent antibodies. Fluorescence was plotted against total DNA content. Cells in S1, S2, S3 and S4 appear respectively in green, red, purple and blue. Four windows indicate cells in S1–S4 and labeled with IdU/CldU.