The ORC/Cdc6/MCM2-7 complex facilitates MCM2-7 dimerization during prereplicative complex formation

Nucleic Acids Res. 2014 Feb;42(4):2257-69. doi: 10.1093/nar/gkt1148. Epub 2013 Nov 14.


The replicative mini-chromosome-maintenance 2-7 (MCM2-7) helicase is loaded in Saccharomyces cerevisiae and other eukaryotes as a head-to-head double-hexamer around origin DNA. At first, ORC/Cdc6 recruits with the help of Cdt1 a single MCM2-7 hexamer to form an 'initial' ORC/Cdc6/Cdt1/MCM2-7 complex. Then, on ATP hydrolysis and Cdt1 release, the 'initial' complex is transformed into an ORC/Cdc6/MCM2-7 (OCM) complex. However, it remains unclear how the OCM is subsequently converted into a MCM2-7 double-hexamer. Through analysis of MCM2-7 hexamer-interface mutants we discovered a complex competent for MCM2-7 dimerization. We demonstrate that these MCM2-7 mutants arrest during prereplicative complex (pre-RC) assembly after OCM formation, but before MCM2-7 double-hexamer assembly. Remarkably, only the OCM complex, but not the 'initial' ORC/Cdc6/Cdt1/MCM2-7 complex, is competent for MCM2-7 dimerization. The MCM2-7 dimer, in contrast to the MCM2-7 double-hexamer, interacts with ORC/Cdc6 and is salt-sensitive, classifying the arrested complex as a helicase-loading intermediate. Accordingly, we found that overexpression of the mutants cause cell-cycle arrest and dominant lethality. Our work identifies the OCM complex as competent for MCM2-7 dimerization, reveals MCM2-7 dimerization as a limiting step during pre-RC formation and defines critical mechanisms that explain how origins are licensed.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Cell Cycle Checkpoints
  • Cell Cycle Proteins / metabolism*
  • DNA Replication*
  • DNA-Binding Proteins / metabolism
  • Minichromosome Maintenance Complex Component 7 / chemistry
  • Minichromosome Maintenance Complex Component 7 / genetics
  • Minichromosome Maintenance Complex Component 7 / metabolism*
  • Minichromosome Maintenance Proteins / chemistry
  • Minichromosome Maintenance Proteins / genetics
  • Minichromosome Maintenance Proteins / metabolism
  • Molecular Sequence Data
  • Mutation
  • Origin Recognition Complex / metabolism*
  • Protein Multimerization
  • Protein Serine-Threonine Kinases / metabolism
  • Saccharomyces cerevisiae / genetics
  • Saccharomyces cerevisiae Proteins / chemistry
  • Saccharomyces cerevisiae Proteins / genetics
  • Saccharomyces cerevisiae Proteins / metabolism*


  • CDC6 protein, S cerevisiae
  • Cell Cycle Proteins
  • DNA-Binding Proteins
  • Origin Recognition Complex
  • Saccharomyces cerevisiae Proteins
  • TAH11 protein, S cerevisiae
  • CDC7 protein, S cerevisiae
  • Protein Serine-Threonine Kinases
  • MCM2 protein, S cerevisiae
  • MCM7 protein, S cerevisiae
  • Minichromosome Maintenance Complex Component 7
  • Minichromosome Maintenance Proteins