Replisome Assembly at oriC, the Replication Origin of E. coli, Reveals an Explanation for Initiation Sites outside an Origin

Fang, Linhua; Davey, Megan J.; O’Donnell, Michael

doi:10.1016/s1097-2765(00)80205-1

Cited by 182 publications

(194 citation statements)

References 49 publications

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“…On the bottom strand the area protected is to the left of DnaA box R1 that overlaps the right 13-mer. Quantitative analysis of this protein complex assembled at oriC supports the conclusion from footprinting studies that two DnaB -DnaC complexes are bound (Fang et al 1999;Carr and Kaguni 2001).…”

Section: Helicase Loading At Oric By Dnaasupporting

confidence: 69%

Helicase Loading at Chromosomal Origins of Replication

Bell

Kaguni

2013

Cold Spring Harbor Perspectives in Biology

115

109

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Loading of the replicative DNA helicase at origins of replication is of central importance in DNA replication. As the first of the replication fork proteins assemble at chromosomal origins of replication, the loaded helicase is required for the recruitment of the rest of the replication machinery. In this work, we review the current knowledge of helicase loading at Escherichia coli and eukaryotic origins of replication. In each case, this process requires both an origin recognition protein as well as one or more additional proteins. Comparison of these events shows intriguing similarities that suggest a similar underlying mechanism, as well as critical differences that likely reflect the distinct processes that regulate helicase loading in bacterial and eukaryotic cells.

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Section: Helicase Loading At Oric By Dnaasupporting

confidence: 69%

Helicase Loading at Chromosomal Origins of Replication

Bell

Kaguni

2013

Cold Spring Harbor Perspectives in Biology

115

109

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“…After E. coli DnaA has melted the AT-rich 13-mers on the left side of oriC, the leftward DnaB helicase is recruited. DnaB must then denature additional DNA before priming and further replisome assembly can occur, including the loading of the rightward helicase (44). In vivo, the first rightward primer was found to have a variable location that was sometimes outside and even to the left of oriC (45), and initiation at the replication origin showed a bias toward its melting side (40), hinting at the bias and stochasticity described here.…”

Section: Discussionmentioning

confidence: 83%

“…In many bacteria, phage , and budding yeast, origins are consistently asymmetric, with a replicator region that binds the initiator protein beside a zone where melting, replisome assembly, and initial priming occur (1,(40)(41)(42)(43). In vitro evidence indicates that the two DnaB hexamers are loaded differentially (44). After E. coli DnaA has melted the AT-rich 13-mers on the left side of oriC, the leftward DnaB helicase is recruited.…”

Section: Discussionmentioning

confidence: 99%

Independence of replisomes in Escherichia coli chromosomal replication

Breier

Cozzarelli

2005

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

102

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In Escherichia coli DNA replication is carried out by the coordinated action of the proteins within a replisome. After replication initiation, the two bidirectionally oriented replisomes from a single origin are colocalized into higher-order structures termed replication factories. The factory model postulated that the two replisomes are also functionally coupled. We tested this hypothesis by using DNA combing and whole-genome microarrays. Nascent DNA surrounding oriC in single, combed chromosomes showed instead that one replisome, usually the leftward one, was significantly ahead of the other 70% of the time. We next used microarrays to follow replication throughout the genome by measuring DNA copy number. We found in multiple E. coli strains that the replisomes are independent, with the leftward replisome ahead of the rightward one. The size of the bias was strain-specific, varying from 50 to 130 kb in the array results. When we artificially blocked one replisome, the other continued unabated, again demonstrating independence. We suggest an improved version of the factory model that retains the advantages of threading DNA through colocalized replisomes at about equal rates, but allows the cell flexibility to overcome obstacles encountered during elongation.DNA combing ͉ microarrays ͉ initiation ͉ replication origin ͉ factory model C ellular DNA replication is almost always initiated in a bidirectional manner. Therefore, initiation of replication requires the recruitment of four polymerases and assorted auxiliary proteins at a replication origin (1). Before 1983, the dominant model was that the leading and lagging polymerases continually and repeatedly sped past each other (Fig. 1A) because of the antiparallel nature of duplex DNA. It was difficult to see how the polymerases could be coordinated to achieve synthesis of both DNA strands at about the same time. Alberts et al. (2) suggested an elegant solution, the trombone model, in which one strand is looped so that the two polymerases are colocalized and point in the same direction (Fig. 1B), forming a replisome that additionally contains the auxiliary proteins. Subsequent work confirmed that sister polymerases are physically attached to one another (1). This colocalization is accompanied by coordination; blocking leading-strand replication stops the whole replisome (3-5).A colocalization of the replisomes themselves was proposed in the factory model of DNA replication (6) and demonstrated cytologically (7). Instead of the left and right replisomes racing away from each other until they meet at the terminus (Fig. 1C), this model proposed that the replisomes have stationary positions in the center of the cell (7). Much as in the trombone model, colocalization is facilitated through looping of the DNA, which is fed through the factory (Fig. 1D). This model organizes replication to the cell's advantage (8,9). Extruding the two daughter chromosomes in opposite directions should greatly facilitate chromosome partitioning (10-12). Furthermore, resources such as dNT...

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“…The E. coli replicative homohexameric DNA helicase DnaB associates with its loader, DnaC, forming a 6:6 complex that is recruited at the chromosomal replication origin (oriC) by the initiator protein DnaA (5). DnaB is then released in an active form, and this initiates formation of two replication forks that extend in opposite directions from oriC (6). Because E. coli DnaB forms stable hexamers in solution that are unable to efficiently selfload onto single-stranded DNA, it was proposed that its loading by DnaC is carried out by a ring-breaking mechanism (1).…”

Section: From the Istituto DI Biochimica Delle Proteine Consiglio Namentioning

confidence: 99%

A CDC6-like Factor from the Archaea Sulfolobus solfataricus Promotes Binding of the Mini-chromosome Maintenance Complex to DNA

Felice

Esposito²,

Pucci³

et al. 2004

Journal of Biological Chemistry

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The archaeal replication apparatus appears to be a simplified version of the eukaryotic one with fewer polypeptides and simpler protein complexes. Herein, we report evidence that a Cdc6-like factor from the hyperthermophilic crenarchaea Sulfolobus solfataricus stimulates binding of the homohexameric MCM-like complex to bubble-and fork-containing DNA oligonucleotides that mimic early replication intermediates. This function does not require the Cdc6 ATP and DNA binding activities. These findings may provide important clues to understanding how the DNA replication initiation process has evolved in the more complex eukaryotic organisms.Living organisms have evolved different strategies to recruit and load DNA helicases at the replication origins, and accessory factors, referred to as helicase loaders, are required to accomplish this task (1, 2). The helicase loading process was best characterized at the molecular level in two bacterial systems: Escherichia coli (3) and Bacillus subtilis (4). The E. coli replicative homohexameric DNA helicase DnaB associates with its loader, DnaC, forming a 6:6 complex that is recruited at the chromosomal replication origin (oriC) by the initiator protein DnaA (5). DnaB is then released in an active form, and this initiates formation of two replication forks that extend in opposite directions from oriC (6). Because E. coli DnaB forms stable hexamers in solution that are unable to efficiently selfload onto single-stranded DNA, it was proposed that its loading by DnaC is carried out by a ring-breaking mechanism (1). A similar ring-opening/closing mechanism was demonstrated to take place during loading of the E. coli phage T7 gp4 DNA helicase/primase, but in this case no accessory loading factor is required (7). In B. subtilis, the replicative DNA helicase DnaC forms homohexamers in solution in the presence of ATP, but without ATP the hexameric form readily dissociates into monomers. The preformed hexameric DnaC helicase is unable to unwind DNA and instead must be assembled from monomers around DNA by a loading system that consists of two proteins, DnaI and DnaB (4). A ring-forming mechanism was also proposed for the E. coli bacteriophage T4 helicase gp41 (8) and for the simian virus 40 large tumor antigen, but in this latter case a separate helicase loader is not required (1, 9).

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Replisome Assembly at oriC, the Replication Origin of E. coli, Reveals an Explanation for Initiation Sites outside an Origin

Cited by 182 publications

References 49 publications

Helicase Loading at Chromosomal Origins of Replication

Helicase Loading at Chromosomal Origins of Replication

Independence of replisomes in Escherichia coli chromosomal replication

A CDC6-like Factor from the Archaea Sulfolobus solfataricus Promotes Binding of the Mini-chromosome Maintenance Complex to DNA

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