A unique DNA entry gate serves for regulated loading of the eukaryotic replicative helicase MCM2-7 onto DNA

作者：Samel Stefan A; Fernandez Cid Alejandra; Sun Jingchuan; Riera Alberto; Tognetti Silvia; Herrera M Carmen; Li Huilin; Speck Christian^*

来源：Genes & Development, 2014, 28(15): 1653-1666.

DOI：10.1101/gad.242404.114

• DNA replication
• replicative helicase
• pre-RC
• DNA licensing
• cancer
• genomic stability

The regulated loading of the replicative helicase minichromosome maintenance proteins 2-7 (MCM2-7) onto replication origins is a prerequisite for replication fork establishment and genomic stability. Origin recognition complex (ORC), Cdc6, and Cdt1 assemble two MCM2-7 hexamers into one double hexamer around dsDNA. Although the MCM2-7 hexamer can adopt a ring shape with a gap between Mcm2 and Mcm5, it is unknown which Mcm interface functions as the DNA entry gate during regulated helicase loading. Here, we establish that the Saccharomyces cerevisiae MCM2-7 hexamer assumes a closed ring structure, suggesting that helicase loading requires active ring opening. Using a chemical biology approach, we show that ORC-Cdc6-Cdt1-dependent helicase loading occurs through a unique DNA entry gate comprised of the Mcm2 and Mcm5 subunits. Controlled inhibition of DNA insertion triggers ATPase-driven complex disassembly in vitro, while in vivo analysis establishes that Mcm2/Mcm5 gate opening is essential for both helicase loading onto chromatin and cell cycle progression. Importantly, we demonstrate that the MCM2-7 helicase becomes loaded onto DNA as a single hexamer during ORC/Cdc6/Cdt1/MCM2-7 complex formation prior to MCM2-7 double hexamer formation. Our study establishes the existence of a unique DNA entry gate for regulated helicase loading, revealing key mechanisms in helicase loading, which has important implications for helicase activation.

• 出版日期2014-8-1