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-Structure paper
Title | DNA unwinding mechanism of a eukaryotic replicative CMG helicase. |
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Journal, issue, pages | Nat Commun, Vol. 11, Issue 1, Page 688, Year 2020 |
Publish date | Feb 4, 2020 |
Authors | Zuanning Yuan / Roxana Georgescu / Lin Bai / Dan Zhang / Huilin Li / Michael E O'Donnell / |
PubMed Abstract | High-resolution structures have not been reported for replicative helicases at a replication fork at atomic resolution, a prerequisite to understanding the unwinding mechanism. The eukaryotic ...High-resolution structures have not been reported for replicative helicases at a replication fork at atomic resolution, a prerequisite to understanding the unwinding mechanism. The eukaryotic replicative CMG (Cdc45, Mcm2-7, GINS) helicase contains a Mcm2-7 motor ring, with the N-tier ring in front and the C-tier motor ring behind. The N-tier ring is structurally divided into a zinc finger (ZF) sub-ring followed by the oligosaccharide/oligonucleotide-binding (OB) fold ring. Here we report the cryo-EM structure of CMG on forked DNA at 3.9 Å, revealing that parental DNA enters the ZF sub-ring and strand separation occurs at the bottom of the ZF sub-ring, where the lagging strand is blocked and diverted sideways by OB hairpin-loops of Mcm3, Mcm4, Mcm6, and Mcm7. Thus, instead of employing a specific steric exclusion process, or even a separation pin, unwinding is achieved via a "dam-and-diversion tunnel" mechanism that does not require specific protein-DNA interaction. The C-tier motor ring contains spirally configured PS1 and H2I loops of Mcms 2, 3, 5, 6 that translocate on the spirally-configured leading strand, and thereby pull the preceding DNA segment through the diversion tunnel for strand separation. |
External links | Nat Commun / PubMed:32019936 / PubMed Central |
Methods | EM (single particle) |
Resolution | 3.9 Å |
Structure data | EMDB-20607, PDB-6u0m: |
Chemicals | ChemComp-ATP: |
Source |
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Keywords | REPLICATION/DNA / DNA replication / CMG-Mcm10 / REPLICATION-DNA complex |