The Human Pre-replication Complex is an Open Complex

Abstract

In eukaryotes, DNA replication initiation requires assembly and activation of the MCM2-7 double hexamer (DH) to melt origin DNA. However, the mechanism for this initial melting is unknown. Here, we report a 2.59-Å cryo-electron microscopy structure of the human MCM-DH (hMCM-DH), also known as pre-replication complex. In this structure, the hMCM-DH showing a constricted central channel untwists and stretches the DNA strands such that almost a half turn of the bound duplex DNA is distorted with one-base pair completely separated, generating an initial open structure (IOS) at the hexamer junction. Disturbing the IOS inhibits MCM-DH formation and replication initiation. High-resolution mapping of hMCM-DH footprints indicates that IOSs are distributed across the human genome in large clusters aligning well with initiation zones designed for robust stochastic origin firing. This work unravels an intrinsic mechanism that couples DH formation with initial DNA melting to license replication initiation in human cells.