Structures of five Rad24-RFC loading intermediates of 9-1-1 clamp, arranged in a plausibly temporary sequence based on the progression of DNA binding in the central chamber of Rad24-RFC. In step 1, the 9-1-1 gate is open, and the DNA has not bound into the clamp loader chamber. In step 2, the 9-1-1 gate remains open, the DNA has entered the central chamber and passed through the 9-1-1- gate, but the DNA is partially stable, and the EM density for 4-bp DNA between the loader and the clamp is missing. In step 3, the 9-1-1 gate remains open, and the DNA in the chamber is fully stabilized. In step 4, the 9-1-1 gate is partially closed, and DNA is fully engaged. In step 5, the 9-1-1 gate is fully closed around the loaded DNA. A representative cryo-EM density map rendered at a high threshold (0.2) is shown at the bottom right corner. For clarity, the Rad24-RFC structure in all five models is in ivory. The red arrow points to the 9-1-1 gate. The DNA entry A gate in Rad24-RFC is labeled in the step 1 structure. The structures are aligned and shown in the same front view.
