Abstract
Two central steps for initiating eukaryotic DNA replication involve loading of the Mcm2-7 helicase onto double-stranded DNA and its activation by GINS-Cdc45. To better understand these events, we determined the structures of Mcm2-7 and the CMG complex by using single-particle electron microscopy. Mcm2-7 adopts two conformations-a lock-washer-shaped spiral state and a planar, gapped-ring form-in which Mcm2 and Mcm5 flank a breach in the helicase perimeter. GINS and Cdc45 bridge this gap, forming a topologically closed assembly with a large interior channel; nucleotide binding further seals off the discontinuity between Mcm2 and Mcm5, partitioning the channel into two smaller pores. Together, our data help explain how GINS and Cdc45 activate Mcm2-7, indicate that Mcm2-7 loading may be assisted by a natural predisposition of the hexamer to form open rings, and suggest a mechanism by which the CMG complex assists DNA strand separation.
Original language | English (US) |
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Pages (from-to) | 471-479 |
Number of pages | 9 |
Journal | Nature Structural and Molecular Biology |
Volume | 18 |
Issue number | 4 |
DOIs | |
State | Published - Apr 2011 |
Externally published | Yes |
ASJC Scopus subject areas
- Structural Biology
- Molecular Biology