Evidence for Sequential and Increasing Activation of Replication Origins along Replication Timing Gradients in the Human Genome
Figure 12
Two alternative models for origins activation along TTRs.
(A) Replication first initiates at early firing origins. Origins fire independently of each other and are specified by an open chromatin structure. (B) Domino model in which replication initiates at early efficient origins. Activation of later origins in less open chromatin is stimulated by approaching replication forks from upstream origins. In both cases (A and B), the rate of origin firing increases during S phase resulting in a U-shaped replication timing profile. Origins of replication are marked by purple circles and black arrows show the direction of replication forks. Color variation (green to red) depicts the chromatin openness. Blue arrows indicate origin stimulation by replication forks from upstream origins.