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Nat Commun. 2016 Feb 18;7:10708. doi: 10.1038/ncomms10708.

Cryo-EM structures of the eukaryotic replicative helicase bound to a translocation substrate.

Author information

1
Macromolecular Machines, Clare Hall Laboratory, The Francis Crick Institute, Blanche Lane, South Mimms EN6 3LD, UK.
2
National Institute for Biological Standards and Control, Microscopy and Imaging, Blanche Lane, South Mimms EN6 3QG, UK.
3
Section of Virology and Single Molecule Imaging Group, Department of Medicine, MRC Clinical Centre, Imperial College London, London W12 0NN, UK.
4
Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Roosevelt Drive, Oxford OX3 7BN, UK.

Abstract

The Cdc45-MCM-GINS (CMG) helicase unwinds DNA during the elongation step of eukaryotic genome duplication and this process depends on the MCM ATPase function. Whether CMG translocation occurs on single- or double-stranded DNA and how ATP hydrolysis drives DNA unwinding remain open questions. Here we use cryo-electron microscopy to describe two subnanometre resolution structures of the CMG helicase trapped on a DNA fork. In the predominant state, the ring-shaped C-terminal ATPase of MCM is compact and contacts single-stranded DNA, via a set of pre-sensor 1 hairpins that spiral around the translocation substrate. In the second state, the ATPase module is relaxed and apparently substrate free, while DNA intimately contacts the downstream amino-terminal tier of the MCM motor ring. These results, supported by single-molecule FRET measurements, lead us to suggest a replication fork unwinding mechanism whereby the N-terminal and AAA+ tiers of the MCM work in concert to translocate on single-stranded DNA.

PMID:
26888060
PMCID:
PMC4759635
DOI:
10.1038/ncomms10708
[Indexed for MEDLINE]
Free PMC Article

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