Eukaryotic DNA replication begins with recruitment of the ring helicase MCM2-7 by the origin recognition complex (ORC) in a reaction facilitated by initiation factors Cdc6 and Cdt1. A new cryo-EM structure of a helicase loading intermediate, the ORC–Cdc6–Cdt1–MCM2-7 complex, unexpectedly reveals both MCM2-7 and ORC hexamers encircling the DNA, and shows the arrangement of all 14 subunits within the helicase-loader complex.
- Jingchuan Sun
- Cecile Evrin
- Huilin Li
