Helicase Activation and Establishment of Replication Forks at Chromosomal Origins of Replication

Tanaka, Seiji; Araki, Hideki

doi:10.1101/cshperspect.a010371

Cited by 154 publications

(149 citation statements)

References 110 publications

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“…In Sulfolobus, GINS is a dimer of dimers: one subunit, Gins23, is related to the eukaryotic GINS components Psf2 and Psf3, and the second Sulfolobus subunit, Gins15, is related to the eukaryotic Sld5 and Psf1. These sequence relationships have been confirmed by structural studies of the Thermococcus kodakarensis GINS complex that have demonstrated the tetrameric assembly of archaeal (Gins15) 2 • (Gins23) 2 and validated the organizational similarity of the archaeal and eukaryotic GINS complexes (15). Interestingly, Sulfolobus GINS copurifies over the course of eight steps with a further polypeptide that we initially named RecJdbh, based on its observed homology with the presumptive DNA binding domain of the bacterial exonuclease, RecJ (8).…”

mentioning

confidence: 72%

“…The sequential recruitment of eukaryal Cdc45 and GINS provide key control points for the cell cycle-dependent regulation of the activation of DNA replication (1,2). This greater regulatory potential in the eukaryal assembly pathway presumably reflects the increased requirement for fidelity of control for the multiplicity of replication origins in eukaryotic chromosomes.…”

Section: Discussionmentioning

confidence: 99%

“…In eukaryotes, origins are defined by the initiator protein ORC complex that, via the actions of two additional factors, the helicase coloaders Cdc6 and Cdt1, directs loading of the MCM(2-7) replicative helicase onto doublestranded DNA. Activation of the MCM(2-7) replicative helicase occurs subsequent to recruitment, leading to DNA melting and assembly of the full replisome apparatus (1,2). Key steps in MCM activation involve a series of phosphorylation-dependent events that promote the sequential association of Cdc45 and the GINS complex with the chromatin-associated MCM double hexamer.…”

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confidence: 99%

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Archaeal orthologs of Cdc45 and GINS form a stable complex that stimulates the helicase activity of MCM

Gristwood²,

Hodgson³

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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The regulated recruitment of Cdc45 and GINS is key to activating the eukaryotic MCM(2-7) replicative helicase. We demonstrate that the homohexameric archaeal MCM helicase associates with orthologs of GINS and Cdc45 in vivo and in vitro. Association of these factors with MCM robustly stimulates the MCM helicase activity. In contrast to the situation in eukaryotes, archaeal Cdc45 and GINS form an extremely stable complex before binding MCM. Further, the archaeal GINS • Cdc45 complex contains two copies of Cdc45. Our analyses give insight into the function and evolution of the conserved core of the archaeal/eukaryotic replisome.T he initiation of DNA replication is an important control point in the progression of the cell cycle. In eukaryotes, origins are defined by the initiator protein ORC complex that, via the actions of two additional factors, the helicase coloaders Cdc6 and Cdt1, directs loading of the MCM(2-7) replicative helicase onto doublestranded DNA. Activation of the MCM(2-7) replicative helicase occurs subsequent to recruitment, leading to DNA melting and assembly of the full replisome apparatus (1, 2). Key steps in MCM activation involve a series of phosphorylation-dependent events that promote the sequential association of Cdc45 and the GINS complex with the chromatin-associated MCM double hexamer. These recruitment events are regulated by the CDK and DDK kinases and require the additional accessory factors Sld3/7, Dpb11, and Sld2(3-6). The Cdc45•MCM(2-7)•GINS complex (CMG) forms the core of the eukaryotic replisome, and this 11-subunit assembly appears to be the functional helicase driving fork progression (3-6). The archaeal replication machinery resembles an ancestral form of its eukaryotic counterpart. Archaea possess a simple homohexameric MCM (5, 7). In addition, archaeal homologs of GINS and Cdc45 have been identified (8)(9)(10)(11)(12)(13)(14). In species of the genus Sulfolobus, we have previously demonstrated that the GINS complex interacts with the N-terminal domains of MCM (8). In Sulfolobus, GINS is a dimer of dimers: one subunit, Gins23, is related to the eukaryotic GINS components Psf2 and Psf3, and the second Sulfolobus subunit, Gins15, is related to the eukaryotic Sld5 and Psf1. These sequence relationships have been confirmed by structural studies of the Thermococcus kodakarensis GINS complex that have demonstrated the tetrameric assembly of archaeal (Gins15) 2 • (Gins23) 2 and validated the organizational similarity of the archaeal and eukaryotic GINS complexes (15). Interestingly, Sulfolobus GINS copurifies over the course of eight steps with a further polypeptide that we initially named RecJdbh, based on its observed homology with the presumptive DNA binding domain of the bacterial exonuclease, RecJ (8). Subsequent sequence analyses have revealed a relationship between RecJ and eukaryotic Cdc45, and this has been elegantly confirmed by recent structural studies of eukaryotic Cdc45 (9,11,16,17). We therefore propose renaming RecJdbh as Cdc45. As archaea lack orthologs of Sld2, Sld...

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confidence: 72%

Section: Discussionmentioning

confidence: 99%

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confidence: 99%

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Archaeal orthologs of Cdc45 and GINS form a stable complex that stimulates the helicase activity of MCM

Gristwood²,

Hodgson³

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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“…R eplicative helicases are hexameric rings in all domains of life (1)(2)(3). In bacteria and archaea, the replicative helicase is a homohexamer and encircles single-strand (ss) DNA at a replication fork.…”

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confidence: 99%

Structure of eukaryotic CMG helicase at a replication fork and implications to replisome architecture and origin initiation

Georgescu

Yuan

Bai

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

180

299

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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 e 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 doublestranded 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.CMG helicase | DNA replication | DNA polymerase | origin initiation | replisome R eplicative helicases are hexameric rings in all domains of life (1-3). In bacteria and archaea, the replicative helicase is a homohexamer and encircles single-strand (ss) DNA at a replication fork. Some viral and phage replicative helicases are also ring-shaped hexamers, including bovine papilloma virus (BPV) E1, simian virus 40 (SV40) large T-antigen (T-Ag), and the T4 and T7 phage helicases. Unlike other replicative helicases, the eukaryotic replicative Mcm2-7 helicase is composed of six nonidentical but homologous Mcm subunits that become activated upon assembly with five accessory factors (Cdc45 and GINS tetramer) to form the 11-subunit CMG (Cdc45, Mcm2-7, GINS) (4-6). Numerous studies have outlined the process that forms CMG at origins in which the Mcm2-7 heterohexamer is loaded onto DNA as an inactive double hexamer in G1 phase, and becomes activated in S phase by several initiation proteins and cell-cycle kinases that assemble Cdc45 and GINS onto Mcm2-7 to form the active CMG helicases (7-9).Helicases assort into six superfamilies (SF1-SF6) based on sequence alignments (10). The SF1 and SF2 helicases are generally monomeric and the SF3-SF6 helicases are hexameric rings used in DNA replication and other processes. The bacterial SF4 and SF5 helicases contain RecA-based motors and translocate 5′-3′, whereas the eukarytic SF3 and SF6 helicases contain AAA+ (ATPases associated with diverse cellular activities)-based motors and translocate 3′-5′ (3, 10). Examples of well-studied hexameric helicases include t...

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“…As cells enter S phase, the combined action of cyclin-dependent kinases and Cdc7-Dbf4 (reviewed in Ref. 40) leads to the formation of a complex between MCM2-7, Cdc45, and GINS (Go, Ichi, Nii, and San) (CMG complex) (41), that bears processive helicase activity (42) and is part of the replisome (43,44).…”

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confidence: 99%

Multi-step Loading of Human Minichromosome Maintenance Proteins in Live Human Cells

Symeonidou

Kotsantis

Roukos

et al. 2013

Journal of Biological Chemistry

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Background: MCM2-7 loading onto chromatin licenses origins for replication. Results: MCMs exhibit transient interactions with chromatin in late mitosis, stable binding in G 1 phase and increased loading in late G 1 phase. Conclusion: Multilevel regulation of MCM2-7 loading to chromatin occurs during mitosis and preceding the G 1 /S phase transition. Significance: The dynamics of the DNA licensing system within live human cells reveal multiple control points.

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Helicase Activation and Establishment of Replication Forks at Chromosomal Origins of Replication

Cited by 154 publications

References 110 publications

Archaeal orthologs of Cdc45 and GINS form a stable complex that stimulates the helicase activity of MCM

Archaeal orthologs of Cdc45 and GINS form a stable complex that stimulates the helicase activity of MCM

Structure of eukaryotic CMG helicase at a replication fork and implications to replisome architecture and origin initiation

Multi-step Loading of Human Minichromosome Maintenance Proteins in Live Human Cells

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