The stereo diagram shows a superposition of domain IV in the closed, intermediate, and open forms (red, blue, and green respectively). The ssDNA for each form is shown in the same coloring scheme. The diagram illustrates that helix O, lying just above the ssDNA, is found in a different conformation in each of the different forms. This helix appears to be responsible for the triggering of the larger domain changes that lead from the closed to the open forms. As the helix moves, the ssDNA moves as well and starts entering the active site. The helices on the top left part of the diagram form part of Domain III, which has already moved in the open form (green). Overall, the only major change observed in Domains I and IV among the three forms is the movement of helix O.