5U8T

Structure of Eukaryotic CMG Helicase at a Replication Fork and Implications

Summary for 5U8T

• Entry DOI: 10.2210/pdb5u8t/pdb
• EMDB information: 8519
• Descriptor: DNA replication licensing factor MCM2, DNA replication complex GINS protein SLD5, Cell division control protein 45, ... (13 entities in total)
• Functional Keywords: cmg helicase, replisome, origin initiation, dna polymerase, dna replication, replication
• Biological source: Saccharomyces cerevisiae (strain ATCC 204508 / S288c) (Baker's yeast); More
• Total number of polymer chains: 12
• Total formula weight: 791714.54

Authors

Li, B.,Georgescu, R.,Yuan, Z.,Santos, R.,Sun, J.,Zhang, D.,Yurieva, O.,Li, H.,O'Donnell, M.E. (deposition date: 2016-12-15, release date: 2017-02-08, Last modification date: 2024-11-20)

Primary citation

Georgescu, R.,Yuan, Z.,Bai, L.,de Luna Almeida Santos, R.,Sun, J.,Zhang, D.,Yurieva, O.,Li, H.,O'Donnell, M.E.
Structure of eukaryotic CMG helicase at a replication fork and implications to replisome architecture and origin initiation.
Proc. Natl. Acad. Sci. U.S.A., 114:E697-E706, 2017

PubMed Abstract: The eukaryotic CMG (Cdc45, Mcm2-7, GINS) helicase consists of the Mcm2-7 hexameric ring along with five accessory factors. The Mcm2-7 heterohexamer, like other hexameric helicases, is shaped like a ring with two tiers, an N-tier ring composed of the N-terminal domains, and a C-tier of C-terminal domains; the C-tier contains the motor. In principle, either tier could translocate ahead of the other during movement on DNA. We have used cryo-EM single-particle 3D reconstruction to solve the structure of CMG in complex with a DNA fork. The duplex stem penetrates into the central channel of the N-tier and the unwound leading single-strand DNA traverses the channel through the N-tier into the C-tier motor, 5'-3' through CMG. Therefore, the N-tier ring is pushed ahead by the C-tier ring during CMG translocation, opposite the currently accepted polarity. The polarity of the N-tier ahead of the C-tier places the leading Pol ε below CMG and Pol α-primase at the top of CMG at the replication fork. Surprisingly, the new N-tier to C-tier polarity of translocation reveals an unforeseen quality-control mechanism at the origin. Thus, upon assembly of head-to-head CMGs that encircle double-stranded DNA at the origin, the two CMGs must pass one another to leave the origin and both must remodel onto opposite strands of single-stranded DNA to do so. We propose that head-to-head motors may generate energy that underlies initial melting at the origin.

PubMed: 28096349
DOI: 10.1073/pnas.1620500114

Experimental method

ELECTRON MICROSCOPY (4.9 Å)