Distribution of ORC1, ORC2, and EdU tracks. (A) This chromatin fiber has an abundance of ORC1 (red signal) and ORC2 (blue signal) proteins, but no EdU tracks. Much of the ORC1 signal appears to be found in streaks (asterisks) rather than in a punctate pattern, indicating multiple copies of this protein are present at these sites. The (B) fiber has regions that appear 'bead-like' (arrows), where DNA replication activity is marked by green EdU labeling. In panel (C), several areas undergoing replication have no overlapping ORC1 or ORC2 proteins (two are marked with arrow heads). These most likely represent sites where ORCs have dissociated from the chromatin. Bars ≅ 25 μm (≅ 400 kb; bottom left of each panel).