Figure 1.

Model to explain the ORC-binding differences between two distinct yeast origin cohorts (24). Origins in the positive-DNA cohort rely on direct interactions between ORC (orange crescent) and the the origin’s ORC binding site to achieve normal levels of ORC binding, while origins in the positive-chromatin cohort require additional interactions with an origin-adjacent protein(s) to achieve normal levels of ORC binding to their intrinsically weak ORC sites. The weaker ORC–DNA interactions at positive-chromatin origins are symbolized with open ORC. In this simple model, a sequence-specific DNA binding protein (green cylinder) binds near the origin and promotes ORC binding (arrow). The arrow is not meant to imply a specific mechanism by which the green factor promotes ORC binding.