In eukaryotes, DNA replication initiation requires assembly and activation of the minichromosome maintenance (MCM) 2–7 double hexamer (DH) to melt origin DNA strands. 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 the pre-replication complex. In this structure, the hMCM-DH with a constricted central channel untwists and stretches the DNA strands such that almost a half turn of the bound duplex DNA is distorted with 1 base pair completely separated, generating an initial open structure (IOS) at the hexamer junction. Disturbing the IOS inhibits DH formation and replication initiation. Mapping of hMCM-DH footprints indicates that IOSs are distributed across the genome in large clusters aligning well with initiation zones designed for stochastic origin firing. This work unravels an intrinsic mechanism that couples DH formation with initial DNA melting to license replication initiation in human cells.
Jian Li, Jiangqing Dong, Weitao Wang, Daqi Yu, Xinyu Fan, Yan Chit Hui, Clare S.K. Lee, Wai Hei Lam, Nathan Alary, Yang Yang, Yingyi Zhang, Qian Zhao, Chun-Long Chen, Bik-Kwoon Tye, Shangyu Dang, Yuanliang Zhai,
The human pre-replication complex is an open complex, Cell, Volume 186, Issue 1, 2023, Pages 98-111.e21, ISSN 0092-8674,