Figure 8.

i-Motif induced deletion models. i-Motifs can form on either the leading or lagging strand depending on the direction of replication. When replication completes, either by restarting replication beyond the leading strand impediment or by replication from a distant replication origin two types of structure are created (20,21,36). A: When an i-motif forms the leading strand impediment and survives after replication deletions occur 5′ to the i-motif on the C-rich strand often extending into the repeat sequence itself. B: When a G-quadruplex forms a transient leading strand impediment and an i-motif forms on the lagging strand, deletions again occur near the i-motif often extending into the repeat sequence itself. Note that when only G-quadruplex survives replication as is the case in dog-1 mutant C. elegans deletions will occur 5′ to the G-quadruplex on the G-rich strand (20,21,36) often extending into the repeat itself.