MCM2-7 Form Double Hexamers at Licensed Origins in Xenopus Egg Extract

J Biol Chem. 2011 Apr 1;286(13):11855-64. doi: 10.1074/jbc.M110.199521. Epub 2011 Jan 31.


In late mitosis and G1, Mcm2-7 are assembled onto replication origins to license them for initiation in the upcoming S phase. After initiation, Mcm2-7 provide helicase activity to unwind DNA at the replication fork. Here we examine the structure of Mcm2-7 on chromatin in Xenopus egg extracts. We show that prior to replication initiation, Mcm2-7 is present at licensed replication origins in a complex with a molecular mass close to double that of the Mcm2-7 hexamer. This complex has approximately stoichiometric quantities of the 6 Mcm2-7 proteins and we conclude that it consists of a double heterohexamer. This provides a configuration potentially capable of initiating a pair of bidirectional replication forks in S phase. We also show that after initiation, Mcm2-7 associate with Cdc45 and GINS to form a relatively stable CMG (Cdc45-MCM-GINS) complex. The CMG proteins also associate less strongly with other replication proteins, consistent with the idea that a single CMG complex forms the core of the replisome.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphatases / genetics
  • Adenosine Triphosphatases / metabolism*
  • Animals
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism*
  • Cell Cycle Proteins / genetics
  • Cell Cycle Proteins / metabolism
  • Cell-Free System
  • Chromatin / metabolism
  • DNA Replication / physiology*
  • G1 Phase / physiology
  • Minichromosome Maintenance Complex Component 2
  • Minichromosome Maintenance Complex Component 7
  • Mitosis / physiology
  • Multiprotein Complexes / genetics
  • Multiprotein Complexes / metabolism*
  • Oocytes / metabolism*
  • Protein Structure, Quaternary
  • Xenopus Proteins / genetics
  • Xenopus Proteins / metabolism*
  • Xenopus laevis


  • Carrier Proteins
  • Cdc45 protein, Xenopus
  • Cell Cycle Proteins
  • Chromatin
  • Multiprotein Complexes
  • Xenopus Proteins
  • Adenosine Triphosphatases
  • Mcm2 protein, Xenopus
  • Mcm7 protein, Xenopus
  • Minichromosome Maintenance Complex Component 2
  • Minichromosome Maintenance Complex Component 7