An ORC/Cdc6/MCM2-7 complex is formed in a multistep reaction to serve as a platform for MCM double-hexamer assembly

Mol Cell. 2013 May 23;50(4):577-88. doi: 10.1016/j.molcel.2013.03.026. Epub 2013 Apr 18.


In Saccharomyces cerevisiae and higher eukaryotes, the loading of the replicative helicase MCM2-7 onto DNA requires the combined activities of ORC, Cdc6, and Cdt1. These proteins load MCM2-7 in an unknown way into a double hexamer around DNA. Here we show that MCM2-7 recruitment by ORC/Cdc6 is blocked by an autoinhibitory domain in the C terminus of Mcm6. Interestingly, Cdt1 can overcome this inhibitory activity, and consequently the Cdt1-MCM2-7 complex activates ORC/Cdc6 ATP-hydrolysis to promote helicase loading. While Cdc6 ATPase activity is known to facilitate Cdt1 release and MCM2-7 loading, we discovered that Orc1 ATP-hydrolysis is equally important in this process. Moreover, we found that Orc1/Cdc6 ATP-hydrolysis promotes the formation of the ORC/Cdc6/MCM2-7 (OCM) complex, which functions in MCM2-7 double-hexamer assembly. Importantly, CDK-dependent phosphorylation of ORC inhibits OCM establishment to ensure once per cell cycle replication. In summary, this work reveals multiple critical mechanisms that redefine our understanding of DNA licensing.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphate / metabolism
  • Binding Sites / genetics
  • Blotting, Western
  • Cell Cycle Proteins / genetics
  • Cell Cycle Proteins / metabolism*
  • Chromosomal Proteins, Non-Histone / genetics
  • Chromosomal Proteins, Non-Histone / metabolism*
  • Cyclin-Dependent Kinases / metabolism
  • DNA, Fungal / genetics
  • DNA, Fungal / metabolism
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism
  • Hydrolysis
  • Models, Biological
  • Multiprotein Complexes / genetics
  • Multiprotein Complexes / metabolism*
  • Mutation
  • Origin Recognition Complex / genetics
  • Origin Recognition Complex / metabolism*
  • Phosphorylation
  • Protein Binding
  • Saccharomyces cerevisiae / genetics
  • Saccharomyces cerevisiae / metabolism
  • Saccharomyces cerevisiae Proteins / genetics
  • Saccharomyces cerevisiae Proteins / metabolism*


  • CDC6 protein, S cerevisiae
  • Cell Cycle Proteins
  • Chromosomal Proteins, Non-Histone
  • DNA, Fungal
  • DNA-Binding Proteins
  • Multiprotein Complexes
  • ORC1 protein, S cerevisiae
  • Origin Recognition Complex
  • Saccharomyces cerevisiae Proteins
  • TAH11 protein, S cerevisiae
  • Adenosine Triphosphate
  • Cyclin-Dependent Kinases
  • MCM2 protein, S cerevisiae