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Structural basis of Mcm2–7 replicative helicase loading by ORC–Cdc6 and Cdt1

Research output: Contribution to journalArticle

  • Zuanning Yuan
  • Alberto Riera
  • Lin Bai
  • Jingchuan Sun
  • Saikat Nandi
  • Christos Spanos
  • Zhuo Angel Chen
  • Marta Barbon
  • Juri Rappsilber
  • Bruce Stillman
  • Christian Speck
  • Huilin Li

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Original languageEnglish
JournalNature Structural & Molecular Biology
Early online date13 Feb 2017
Publication statusPublished - Mar 2017


To initiate DNA replication, the origin recognition complex (ORC) and Cdc6 load an Mcm2–7 double hexamer onto DNA. Without ATP hydrolysis, ORC–Cdc6 recruits one Cdt1-bound Mcm2–7 hexamer, thus forming an ORC–Cdc6–Cdt1–Mcm2–7 (OCCM) helicase-loading intermediate. Here we report a 3.9-Å structure of Saccharomyces cerevisiae OCCM on DNA. Flexible Mcm2–7 winged-helix domains (WHDs) engage ORC–Cdc6. A three-domain Cdt1 configuration embraces Mcm2, Mcm4, and Mcm6, thus comprising nearly half of the hexamer. The Cdt1 C-terminal domain extends to the Mcm6 WHD, which binds the Orc4 WHD. DNA passes through the ORC–Cdc6 and Mcm2–7 rings. Origin DNA interaction is mediated by an α-helix within Orc4 and positively charged loops within Orc2 and Cdc6. The Mcm2–7 C-tier AAA+ ring is topologically closed by an Mcm5 loop that embraces Mcm2, but the N-tier-ring Mcm2-Mcm5 interface remains open. This structure suggests a loading mechanism of the first Cdt1-bound Mcm2–7 hexamer by ORC–Cdc6.

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