Figure 3.

Capturing the loading intermediates OCM and OCMM by direct mixing and cross‐linking. A: Cryo‐EM 2D class averages of OCCM in 1 mM ATPγS. B−D: Four class averages of three loading intermediates observed by negative stain EM in 1 mM ATP: OCM (B), OCMM (C), and the Mcm2‐7 double hexamer (D). Note that panel (C) for OCMM is on a smaller scale. Scale bar is 20 nm. E: A sketch showing that OCM is the loader of the second Cdt1 bound Mcm2‐7 hexamer, and OCMM is an on‐pathway intermediate for the double hexamer assembly. ORC is in orange, Cdc6 in cyan, Cdt1 in green, and Mcm2‐7 in purple. The dsDNA is shown as a blue line.