Mechanism and timing of Mcm2-7 ring closure during DNA replication origin licensing

• Main Authors: Ticau, Simina (Contributor), Friedman, Larry J (Author), Champasa, Kanokwan (Contributor), Corrêa, Ivan R (Author), Gelles, Jeff (Author), Bell, Stephen P (Contributor)
• Other Authors: Massachusetts Institute of Technology. Department of Biology (Contributor)
• Format: Article
• Language: English
• Published: Springer Nature, 2018-06-21T13:50:39Z.
• Subjects: Article
• Online Access: Get fulltext

 The opening and closing of two ring-shaped Mcm2-7 DNA helicases is necessary to license eukaryotic origins of replication, although the mechanisms controlling these events are unclear. The origin-recognition complex (ORC), Cdc6 and Cdt1 facilitate this process by establishing a topological link between each Mcm2-7 hexamer and origin DNA. Using colocalization single-molecule spectroscopy and single-molecule Förster resonance energy transfer (FRET), we monitored ring opening and closing of Saccharomyces cerevisiae Mcm2-7 during origin licensing. The two Mcm2-7 rings were open during initial DNA association and closed sequentially, concomitant with the release of their associated Cdt1. We observed that ATP hydrolysis by Mcm2-7 was coupled to ring closure and Cdt1 release, and failure to load the first Mcm2-7 prevented recruitment of the second Mcm2-7. Our findings identify key mechanisms controlling the Mcm2-7 DNA-entry gate during origin licensing, and reveal that the two Mcm2-7 complexes are loaded via a coordinated series of events with implications for bidirectional replication initiation and quality control.