title: MCM2-7 form double hexamers at licensed origins in Xenopus egg extract.
abstract: 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.
authors.affiliation: Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, United Kingdom.
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Gambus
authors.forename: Guennadi A
authors.initials: GA
authors.lastname: Khoudoli
authors.forename: Richard C
authors.initials: RC
authors.lastname: Jones
authors.forename: J Julian
authors.initials: JJ
authors.lastname: Blow
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002474:Cell-Free System; D002843:Chromatin / Q000378:metabolism; D004261:DNA Replication / Q000502:physiology*; D016193:G1 Phase / Q000502:physiology; D064111:Minichromosome Maintenance Complex Component 2; D064168:Minichromosome Maintenance Complex Component 7; D008938:Mitosis / Q000502:physiology; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism*; D020836:Protein Structure, Quaternary; D029867:Xenopus Proteins / Q000235:genetics / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: D002352:Carrier Proteins; C502211:Cdc45 protein, Xenopus; D018797:Cell Cycle Proteins; D002843:Chromatin; D046912:Multiprotein Complexes; D029867:Xenopus Proteins; D000251:Adenosine Triphosphatases; C102186:Mcm2 protein, Xenopus; C509836:Mcm7 protein, Xenopus; D064111:Minichromosome Maintenance Complex Component 2; D064168:Minichromosome Maintenance Complex Component 7