401
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Fu YV, Yardimci H, Long DT, Ho TV, Guainazzi A, Bermudez VP, Hurwitz J, van Oijen A, Schärer OD, Walter JC. Selective bypass of a lagging strand roadblock by the eukaryotic replicative DNA helicase. Cell 2011; 146:931-41. [PMID: 21925316 DOI: 10.1016/j.cell.2011.07.045] [Citation(s) in RCA: 296] [Impact Index Per Article: 21.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2010] [Revised: 05/17/2011] [Accepted: 07/29/2011] [Indexed: 12/13/2022]
Abstract
The eukaryotic replicative DNA helicase, CMG, unwinds DNA by an unknown mechanism. In some models, CMG encircles and translocates along one strand of DNA while excluding the other strand. In others, CMG encircles and translocates along duplex DNA. To distinguish between these models, replisomes were confronted with strand-specific DNA roadblocks in Xenopus egg extracts. An ssDNA translocase should stall at an obstruction on the translocation strand but not the excluded strand, whereas a dsDNA translocase should stall at obstructions on either strand. We found that replisomes bypass large roadblocks on the lagging strand template much more readily than on the leading strand template. Our results indicate that CMG is a 3' to 5' ssDNA translocase, consistent with unwinding via "steric exclusion." Given that MCM2-7 encircles dsDNA in G1, the data imply that formation of CMG in S phase involves remodeling of MCM2-7 from a dsDNA to a ssDNA binding mode.
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Affiliation(s)
- Yu V Fu
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
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402
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Multiple Cdt1 molecules act at each origin to load replication-competent Mcm2-7 helicases. EMBO J 2011; 30:4885-96. [PMID: 22045335 DOI: 10.1038/emboj.2011.394] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2011] [Accepted: 10/06/2011] [Indexed: 11/08/2022] Open
Abstract
Eukaryotic origins of replication are selected by loading a head-to-head double hexamer of the Mcm2-7 replicative helicase around origin DNA. Cdt1 plays an essential but transient role during this event; however, its mechanism of action is unknown. Through analysis of Cdt1 mutations, we demonstrate that Cdt1 performs multiple functions during helicase loading. The C-terminus of Cdt1 binds Mcm2-7, and this interaction is required for efficient origin recruitment of both proteins. We show that origin recognition complex (ORC) and Cdc6 recruit multiple Cdt1 molecules to the origin during helicase loading, and disruption of this multi-Cdt1 intermediate prevents helicase loading. Although dispensable for loading Mcm2-7 double hexamers that are topologically linked to DNA, the essential N-terminal domain of Cdt1 is required to load Mcm2-7 complexes that are competent for association with the Cdc45 and GINS helicase-activating proteins and replication initiation. Our data support a model in which origin-bound ORC and Cdc6 recruit two Cdt1 molecules to initiate double-hexamer formation prior to helicase loading and demonstrate that Cdt1 influences the replication competence of loaded Mcm2-7 helicases.
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403
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Li JJ, Schnick J, Hayles J, MacNeill SA. Purification and functional inactivation of the fission yeast MCM(MCM-BP) complex. FEBS Lett 2011; 585:3850-5. [PMID: 22036784 DOI: 10.1016/j.febslet.2011.10.033] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2011] [Revised: 10/09/2011] [Accepted: 10/14/2011] [Indexed: 12/31/2022]
Abstract
The MCM (mini-chromosome maintenance) complex is the core of the eukaryotic replicative helicase and comprises six proteins, Mcm2-Mcm7. In humans, a variant form of the complex has Mcm2 replaced by the MCM-BP protein. Recent results suggest that a similar complex exists in fission yeast with an essential role in DNA replication and cell cycle progression. Here, we describe the purification and subunit composition of the fission yeast MCM(Mcb1) complex. Using newly generated temperature-sensitive alleles, we show that loss of MCM(Mcb1) function leads to accumulation of DNA damage, checkpoint activation and cell cycle arrest, and provide evidence for a role for MCM(Mcb1) in meiosis.
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Affiliation(s)
- Juan-juan Li
- Cancer Research UK London Research Institute, London, UK
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404
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Franz A, Orth M, Pirson PA, Sonneville R, Blow JJ, Gartner A, Stemmann O, Hoppe T. CDC-48/p97 coordinates CDT-1 degradation with GINS chromatin dissociation to ensure faithful DNA replication. Mol Cell 2011; 44:85-96. [PMID: 21981920 PMCID: PMC3428722 DOI: 10.1016/j.molcel.2011.08.028] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2011] [Revised: 06/22/2011] [Accepted: 08/03/2011] [Indexed: 01/28/2023]
Abstract
Faithful transmission of genomic information requires tight spatiotemporal regulation of DNA replication factors. In the licensing step of DNA replication, CDT-1 is loaded onto chromatin to subsequently promote the recruitment of additional replication factors, including CDC-45 and GINS. During the elongation step, the CDC-45/GINS complex moves with the replication fork; however, it is largely unknown how its chromatin association is regulated. Here, we show that the chaperone-like ATPase CDC-48/p97 coordinates degradation of CDT-1 with release of the CDC-45/GINS complex. C. elegans embryos lacking CDC-48 or its cofactors UFD-1/NPL-4 accumulate CDT-1 on mitotic chromatin, indicating a critical role of CDC-48 in CDT-1 turnover. Strikingly, CDC-48(UFD-1/NPL-4)-deficient embryos show persistent chromatin association of CDC-45/GINS, which is a consequence of CDT-1 stabilization. Moreover, our data confirmed a similar regulation in Xenopus egg extracts, emphasizing a conserved coordination of licensing and elongation events during eukaryotic DNA replication by CDC-48/p97.
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Affiliation(s)
- André Franz
- Institute for Genetics and Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases (CECAD) University of Cologne Zülpicher Str. 47a 50674 Cologne, Germany
| | - Michael Orth
- Department of Genetics, University of Bayreuth, Universitätsstrasse 30, 95440 Bayreuth, Germany
| | - Paul A. Pirson
- Institute for Genetics and Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases (CECAD) University of Cologne Zülpicher Str. 47a 50674 Cologne, Germany
| | - Remi Sonneville
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Scotland
| | - J. Julian Blow
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Scotland
| | - Anton Gartner
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Scotland
| | - Olaf Stemmann
- Department of Genetics, University of Bayreuth, Universitätsstrasse 30, 95440 Bayreuth, Germany
| | - Thorsten Hoppe
- Institute for Genetics and Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases (CECAD) University of Cologne Zülpicher Str. 47a 50674 Cologne, Germany
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405
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Heller RC, Kang S, Lam WM, Chen S, Chan CS, Bell SP. Eukaryotic origin-dependent DNA replication in vitro reveals sequential action of DDK and S-CDK kinases. Cell 2011; 146:80-91. [PMID: 21729781 DOI: 10.1016/j.cell.2011.06.012] [Citation(s) in RCA: 252] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2010] [Revised: 04/12/2011] [Accepted: 06/07/2011] [Indexed: 11/28/2022]
Abstract
Proper eukaryotic DNA replication requires temporal separation of helicase loading from helicase activation and replisome assembly. Using an in vitro assay for eukaryotic origin-dependent replication initiation, we investigated the control of these events. After helicase loading, we found that the Dbf4-dependent Cdc7 kinase (DDK) but not S phase cyclin-dependent kinase (S-CDK) is required for the initial origin recruitment of Sld3 and the Cdc45 helicase-activating protein. Likewise, in vivo, DDK drives early-firing-origin recruitment of Cdc45 before activation of S-CDK. After S-CDK activation, a second helicase-activating protein (GINS) and the remainder of the replisome are recruited to the origin. Finally, recruitment of lagging but not leading strand DNA polymerases depends on Mcm10 and DNA unwinding. Our studies identify distinct roles for DDK and S-CDK during helicase activation and support a model in which the leading strand DNA polymerase is recruited prior to origin DNA unwinding and RNA primer synthesis.
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Affiliation(s)
- Ryan C Heller
- Howard Hughes Medical Institute, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
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406
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Bruck I, Kanter DM, Kaplan DL. Enabling association of the GINS protein tetramer with the mini chromosome maintenance (Mcm)2-7 protein complex by phosphorylated Sld2 protein and single-stranded origin DNA. J Biol Chem 2011; 286:36414-26. [PMID: 21868389 DOI: 10.1074/jbc.m111.282822] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The Cdc45-Mcm2-7-GINS (CMG) complex is the replication fork helicase in eukaryotes. Synthetic lethal with Dpb11-1 (Sld2) is required for the initiation of DNA replication, and the S phase cyclin-dependent kinase (S-CDK) phosphorylates Sld2 in vivo. We purified components of the replication initiation machinery and studied their interactions in vitro. We found that unphosphorylated or CDK-phosphorylated Sld2 binds to the mini chromosome maintenance (Mcm)2-7 complex with similar efficiency. Sld2 interaction with Mcm2-7 blocks the interaction between GINS and Mcm2-7. The interaction between CDK-phosphorylated Sld2 and Mcm2-7 is substantially inhibited by origin single-stranded DNA (ssDNA). Furthermore, origin ssDNA allows GINS to bind to Mcm2-7 in the presence of CDK-phosphorylated Sld2. However, unphosphorylated Sld2 blocks the interaction between GINS and Mcm2-7 even in the presence of origin ssDNA. We identified a mutant of Sld2 that does not bind to DNA. When this mutant is expressed in yeast cells, cell growth is severely inhibited with very slow progression into S phase. We propose a model wherein Sld2 blocks the interaction between GINS and Mcm2-7 in vivo. Once origin ssDNA is extruded from the Mcm2-7 ring and CDK phosphorylates Sld2, the origin ssDNA binds to CDK-phosphorylated Sld2. This event may allow the interaction between GINS and Mcm2-7 in vivo. Thus, CDK phosphorylation of Sld2 may be important to release Sld2 from Mcm2-7, thereby allowing GINS to bind Mcm2-7. Furthermore, origin ssDNA may stimulate the formation of the CMG complex by alleviating inhibitory interactions between Sld2 with Mcm2-7.
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Affiliation(s)
- Irina Bruck
- Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee 37235, USA
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407
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Pan M, Santangelo TJ, Li Z, Reeve JN, Kelman Z. Thermococcus kodakarensis encodes three MCM homologs but only one is essential. Nucleic Acids Res 2011; 39:9671-80. [PMID: 21821658 PMCID: PMC3239210 DOI: 10.1093/nar/gkr624] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
The minichromosome maintenance (MCM) complex is thought to function as the replicative helicase in archaea and eukaryotes. In eukaryotes, this complex is an assembly of six different but related polypeptides (MCM2-7) but, in most archaea, one MCM protein assembles to form a homohexameric complex. Atypically, the Thermococcus kodakarensis genome encodes three archaeal MCM homologs, here designated MCM1-3, although MCM1 and MCM2 are unusual in having long and unique N-terminal extensions. The results reported establish that MCM2 and MCM3 assemble into homohexamers and exhibit DNA binding, helicase and ATPase activities in vitro typical of archaeal MCMs. In contrast, MCM1 does not form homohexamers and although MCM1 binds DNA and has ATPase activity, it has only minimal helicase activity in vitro. Removal of the N-terminal extension had no detectable effects on MCM1 but increased the helicase activity of MCM2. A T. kodakarensis strain with the genes TK0096 (MCM1) and TK1361 (MCM2) deleted has been constructed that exhibits no detectable defects in growth or viability, but all attempts to delete TK1620 (MCM3) have been unsuccessful arguing that that MCM3 is essential and is likely the replicative helicase in T. kodakarensis. The origins and possible function(s) of the three MCM proteins are discussed.
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Affiliation(s)
- Miao Pan
- Institute for Bioscience and Biotechnology Research, University of Maryland, 9600 Gudelsky Drive, Rockville, MD 20850, USA
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408
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Ding L, Forsburg SL. Schizosaccharomyces pombe minichromosome maintenance-binding protein (MCM-BP) antagonizes MCM helicase. J Biol Chem 2011; 286:32918-30. [PMID: 21813639 DOI: 10.1074/jbc.m111.282541] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The minichromosome maintenance (MCM) complex, a replicative helicase, is a heterohexamer essential for DNA duplication and genome stability. We identified Schizosaccharomyces pombe mcb1(+) (Mcm-binding protein 1), an apparent orthologue of the human MCM-binding protein that associates with a subset of MCM complex proteins. mcb1(+) is an essential gene. Deletion of mcb1(+) caused cell cycle arrest after several generations with a cdc phenotype and disrupted nuclear structure. Mcb1 is an abundant protein, constitutively present across the cell cycle. It is widely distributed in cytoplasm and nucleoplasm and bound to chromatin. Co-immunoprecipitation suggested that Mcb1 interacts robustly with Mcm3-7 but not Mcm2. Overproduction of Mcb1 disrupted the association of Mcm2 with other MCM proteins, resulting in inhibition of DNA replication, DNA damage, and activation of the checkpoint kinase Chk1. Thus, Mcb1 appears to antagonize the function of MCM helicase.
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Affiliation(s)
- Lin Ding
- Molecular and Computational Biology Program, University of Southern California, Los Angeles, California 90089-2910, USA
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409
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Graham BW, Schauer GD, Leuba SH, Trakselis MA. Steric exclusion and wrapping of the excluded DNA strand occurs along discrete external binding paths during MCM helicase unwinding. Nucleic Acids Res 2011; 39:6585-95. [PMID: 21576224 PMCID: PMC3159478 DOI: 10.1093/nar/gkr345] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2011] [Revised: 04/25/2011] [Accepted: 04/26/2011] [Indexed: 11/17/2022] Open
Abstract
The minichromosome maintenance (MCM) helicase complex is essential for the initiation and elongation of DNA replication in both the eukaryotic and archaeal domains. The archaeal homohexameric MCM helicase from Sulfolobus solfataricus serves as a model for understanding mechanisms of DNA unwinding. In this report, the displaced 5'-tail is shown to provide stability to the MCM complex on DNA and contribute to unwinding. Mutations in a positively charged patch on the exterior surface of the MCM hexamer destabilize this interaction, alter the path of the displaced 5'-tail DNA and reduce unwinding. DNA footprinting and single-molecule fluorescence experiments support a previously unrecognized wrapping of the 5'-tail. This mode of hexameric helicase DNA unwinding is termed the steric exclusion and wrapping (SEW) model, where the 3'-tail is encircled by the helicase while the displaced 5'-tail wraps around defined paths on the exterior of the helicase. The novel wrapping mechanism stabilizes the MCM complex in a positive unwinding mode, protects the displaced single-stranded DNA tail and prevents reannealing.
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Affiliation(s)
- Brian W. Graham
- Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260 and Department of Cell Biology and Physiology, Hillman Cancer Center, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - Grant D. Schauer
- Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260 and Department of Cell Biology and Physiology, Hillman Cancer Center, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - Sanford H. Leuba
- Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260 and Department of Cell Biology and Physiology, Hillman Cancer Center, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - Michael A. Trakselis
- Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260 and Department of Cell Biology and Physiology, Hillman Cancer Center, University of Pittsburgh, Pittsburgh, PA 15213, USA
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410
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Dang HQ, Li Z. The Cdc45·Mcm2-7·GINS protein complex in trypanosomes regulates DNA replication and interacts with two Orc1-like proteins in the origin recognition complex. J Biol Chem 2011; 286:32424-35. [PMID: 21799014 DOI: 10.1074/jbc.m111.240143] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Accurate DNA replication requires a complex interplay of many regulatory proteins at replication origins. The CMG (Cdc45·Mcm2-7·GINS) complex, which is composed of Cdc45, Mcm2-7, and the GINS (Go-Ichi-Ni-San) complex consisting of Sld5 and Psf1 to Psf3, is recruited by Cdc6 and Cdt1 onto origins bound by the heterohexameric origin recognition complex (ORC) and functions as a replicative helicase. Trypanosoma brucei, an early branched microbial eukaryote, appears to express an archaea-like ORC consisting of a single Orc1/Cdc6-like protein. However, unlike archaea, trypanosomes possess components of the eukaryote-like CMG complex, but whether they form an active helicase complex, associate with the ORC, and regulate DNA replication remains unknown. Here, we demonstrated that the CMG complex is formed in vivo in trypanosomes and that Mcm2-7 helicase activity is activated by the association with Cdc45 and the GINS complex in vitro. Mcm2-7 and GINS proteins are confined to the nucleus throughout the cell cycle, whereas Cdc45 is exported out of the nucleus after DNA replication, indicating that nuclear exclusion of Cdc45 constitutes one mechanism for preventing DNA re-replication in trypanosomes. With the exception of Mcm4, Mcm6, and Psf1, knockdown of individual CMG genes inhibits DNA replication and cell proliferation. Finally, we identified a novel Orc1-like protein, Orc1b, as an additional component of the ORC and showed that both Orc1b and Orc1/Cdc6 associate with Mcm2-7 via interactions with Mcm3. All together, we identified the Cdc45·Mcm2-7·GINS complex as the replicative helicase that interacts with two Orc1-like proteins in the unusual origin recognition complex in trypanosomes.
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Affiliation(s)
- Hung Quang Dang
- Department of Microbiology and Molecular Genetics, University of Texas Medical School, Houston, Texas 77030, USA
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411
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Sharma A, Kar A, Kaur M, Ranade SM, Sankaran A, Misra S, Rawat K, Saxena S. Specific replication factors are targeted by different genotoxic agents to inhibit replication. IUBMB Life 2011; 62:764-75. [PMID: 20945455 DOI: 10.1002/iub.380] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
When mammalian cells experience DNA damaging stress, they block DNA replication to avoid erroneous replication of the damaged template. The cells that are unable to respond to DNA damage continue faulty DNA replication that results in incorporation of genomic lesions. To understand the regulation of replication machinery during stress, systemic studies have been carried out but they have been restricted to the evaluation of the mRNA levels and therefore have not been able to identify post-transcriptional changes, vital for immediate blocking of the progressing DNA replication. We have recently discovered that an essential replication factor is downregulated by radiation stress. In this study, we have carried out a systematic evaluation of protein levels of entire replication apparatus after different types of DNA damage. We report that, independent of the status of p53 and retinoblastoma protein, mammalian cells choose targets that are essential for prereplication, preinitiation, and elongation phases of replication. We imposed different kinds of stress to discern whether similar or unique responses are invoked, and we propose a model for inhibition of replication machinery in which mammalian cells target specific essential replication factors based on the experienced stress.
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Affiliation(s)
- Aparna Sharma
- National Institute of Immunology, Aruna Asaf Ali Marg, New Delhi, India
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412
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How dormant origins promote complete genome replication. Trends Biochem Sci 2011; 36:405-14. [PMID: 21641805 DOI: 10.1016/j.tibs.2011.05.002] [Citation(s) in RCA: 174] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2011] [Revised: 04/26/2011] [Accepted: 05/04/2011] [Indexed: 01/21/2023]
Abstract
Many replication origins that are licensed by loading MCM2-7 complexes in G1 are not normally used. Activation of these dormant origins during S phase provides a first line of defence for the genome if replication is inhibited. When replication forks fail, dormant origins are activated within regions of the genome currently engaged in replication. At the same time, DNA damage-response kinases activated by the stalled forks preferentially suppress the assembly of new replication factories, thereby ensuring that chromosomal regions experiencing replicative stress complete synthesis before new regions of the genome are replicated. Mice expressing reduced levels of MCM2-7 have fewer dormant origins, are cancer-prone and are genetically unstable, demonstrating the importance of dormant origins for preserving genome integrity. We review the function of dormant origins, the molecular mechanism of their regulation and their physiological implications.
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413
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Kumagai A, Shevchenko A, Shevchenko A, Dunphy WG. Direct regulation of Treslin by cyclin-dependent kinase is essential for the onset of DNA replication. ACTA ACUST UNITED AC 2011; 193:995-1007. [PMID: 21646402 PMCID: PMC3115804 DOI: 10.1083/jcb.201102003] [Citation(s) in RCA: 101] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Treslin, a TopBP1-interacting protein, is necessary for deoxyribonucleic acid (DNA) replication in vertebrates. Association between Treslin and TopBP1 requires cyclin-dependent kinase (Cdk) activity in Xenopus laevis egg extracts. We investigated the mechanism and functional importance of Cdk for this interaction using both X. laevis egg extracts and human cells. We found that Treslin also associated with TopBP1 in a Cdk-regulated manner in human cells and that Treslin was phosphorylated within a conserved Cdk consensus target sequence (on S976 in X. laevis and S1000 in humans). Recombinant human Cdk2-cyclin E also phosphorylated this residue of Treslin in vitro very effectively. Moreover, a mutant of Treslin that cannot undergo phosphorylation on this site showed significantly diminished binding to TopBP1. Finally, human cells harboring this mutant were severely deficient in DNA replication. Collectively, these results indicate that Cdk-mediated phosphorylation of Treslin during S phase is necessary for both its effective association with TopBP1 and its ability to promote DNA replication in human cells.
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Affiliation(s)
- Akiko Kumagai
- Division of Biology, California Institute of Technology, Pasadena, CA 91125, USA
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414
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Abstract
GINS is an essential eukaryotic DNA replication factor that is found in a simplified form in Archaea. A new study in this issue of BMC Biology reveals the first structure of the archaeal GINS complex. The structure reveals the anticipated similarity to the previously determined eukaryotic complex but also has some intriguing differences in the relative disposition of subunit domains. See research article: http://www.biomedcentral.com/1741-7007/9/28
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Affiliation(s)
- Stephen D Bell
- Sir William Dunn School of Pathology, Oxford OX1 3RE, UK.
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415
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Toyokawa G, Masuda K, Daigo Y, Cho HS, Yoshimatsu M, Takawa M, Hayami S, Maejima K, Chino M, Field HI, Neal DE, Tsuchiya E, Ponder BAJ, Maehara Y, Nakamura Y, Hamamoto R. Minichromosome Maintenance Protein 7 is a potential therapeutic target in human cancer and a novel prognostic marker of non-small cell lung cancer. Mol Cancer 2011; 10:65. [PMID: 21619671 PMCID: PMC3125391 DOI: 10.1186/1476-4598-10-65] [Citation(s) in RCA: 95] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2011] [Accepted: 05/28/2011] [Indexed: 12/24/2022] Open
Abstract
BACKGROUND The research emphasis in anti-cancer drug discovery has always been to search for a drug with the greatest antitumor potential but fewest side effects. This can only be achieved if the drug used is against a specific target located in the tumor cells. In this study, we evaluated Minichromosome Maintenance Protein 7 (MCM7) as a novel therapeutic target in cancer. RESULTS Immunohistochemical analysis showed that MCM7 was positively stained in 196 of 331 non-small cell lung cancer (NSCLC), 21 of 29 bladder tumor and 25 of 70 liver tumor cases whereas no significant staining was observed in various normal tissues. We also found an elevated expression of MCM7 to be associated with poor prognosis for patients with NSCLC (P = 0.0055). qRT-PCR revealed a higher expression of MCM7 in clinical bladder cancer tissues than in corresponding non-neoplastic tissues (P < 0.0001), and we confirmed that a wide range of cancers also overexpressed MCM7 by cDNA microarray analysis. Suppression of MCM7 using specific siRNAs inhibited incorporation of BrdU in lung and bladder cancer cells overexpressing MCM7, and suppressed the growth of those cells more efficiently than that of normal cell strains expressing lower levels of MCM7. CONCLUSIONS Since MCM7 expression was generally low in a number of normal tissues we examined, MCM7 has the characteristics of an ideal candidate for molecular targeted cancer therapy in various tumors and also as a good prognostic biomarker for NSCLC patients.
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Affiliation(s)
- Gouji Toyokawa
- Laboratory of Molecular Medicine, Human Genome Center, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan
- Department of Surgery and Science, Graduate School of Medical Science, Kyusyu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
| | - Ken Masuda
- Laboratory of Molecular Medicine, Human Genome Center, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan
| | - Yataro Daigo
- Laboratory of Molecular Medicine, Human Genome Center, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan
- Department of Medical Oncology, Shiga University of Medical Science, Otsu 520-2192, Japan
| | - Hyun-Soo Cho
- Laboratory of Molecular Medicine, Human Genome Center, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan
| | - Masanori Yoshimatsu
- Laboratory of Molecular Medicine, Human Genome Center, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan
- Department of Surgery and Science, Graduate School of Medical Science, Kyusyu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
| | - Masashi Takawa
- Laboratory of Molecular Medicine, Human Genome Center, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan
| | - Shinya Hayami
- Laboratory of Molecular Medicine, Human Genome Center, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan
| | - Kazuhiro Maejima
- Laboratory of Molecular Medicine, Human Genome Center, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan
| | - Makoto Chino
- Specialty Chemicals & International Division Pharmaceuticals Group, Nippon Kayaku Co., Ltd., 11-2, Fujimi 1 Chome, Chiyoda-ku, Tokyo, 102-8172, Japan
| | - Helen I Field
- Department of Genetics, University of Cambridge, Downing Street, Cambridge CB2 3EH, UK
| | - David E Neal
- Department of Oncology, Cancer Research UK Cambridge Research Institute, University of Cambridge, Robinson Way, Cambridge CB2 0RE, UK
| | - Eiju Tsuchiya
- Department of Pathology, Saitama Cancer Center, Saitama 362-0806, Japan
- Molecular Pathology and Genetics Division, Kanagawa Cancer Center Research Institute, Kanagawa 241-0815, Japan
| | - Bruce AJ Ponder
- Department of Oncology, Cancer Research UK Cambridge Research Institute, University of Cambridge, Robinson Way, Cambridge CB2 0RE, UK
| | - Yoshihiko Maehara
- Department of Surgery and Science, Graduate School of Medical Science, Kyusyu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
| | - Yusuke Nakamura
- Laboratory of Molecular Medicine, Human Genome Center, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan
| | - Ryuji Hamamoto
- Laboratory of Molecular Medicine, Human Genome Center, Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan
- Department of Oncology, Cancer Research UK Cambridge Research Institute, University of Cambridge, Robinson Way, Cambridge CB2 0RE, UK
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416
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Bruck I, Kaplan DL. Origin single-stranded DNA releases Sld3 protein from the Mcm2-7 complex, allowing the GINS tetramer to bind the Mcm2-7 complex. J Biol Chem 2011; 286:18602-13. [PMID: 21460226 PMCID: PMC3099676 DOI: 10.1074/jbc.m111.226332] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2011] [Revised: 03/25/2011] [Indexed: 11/06/2022] Open
Abstract
The replication fork helicase in eukaryotic cells is comprised of Cdc45, Mcm2-7, and GINS (CMG complex). In budding yeast, Sld3, Sld2, and Dpb11 are required for the initiation of DNA replication, but Sld3 and Dpb11 do not travel with the replication fork. Sld3 and Cdc45 bind to early replication origins during the G(1) phase of the cell cycle, whereas Sld2, GINS, polymerase ε, and Dpb11 form a transient preloading complex that associates with origins during S phase. We show here that Sld3 binds tightly to origin single-stranded DNA (ssDNA). CDK-phosphorylated Sld3 binds to origin ssDNA with similar high affinity. Origin ssDNA does not disrupt the interaction between Sld3 and Dpb11, and origin ssDNA does not disrupt the interaction between Sld3 and Cdc45. However, origin ssDNA substantially disrupts the interaction between Sld3 and Mcm2-7. GINS and Sld3 compete with one another for binding to Mcm2-7. However, in a mixture of Sld3, GINS, and Mcm2-7, origin ssDNA inhibits the interaction between Sld3 and Mcm2-7, whereas origin ssDNA promotes the association between GINS and Mcm2-7. We also show that origin single-stranded DNA promotes the formation of the CMG complex. We conclude that origin single-stranded DNA releases Sld3 from Mcm2-7, allowing GINS to bind Mcm2-7.
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Affiliation(s)
- Irina Bruck
- From the Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee 37235
| | - Daniel L. Kaplan
- From the Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee 37235
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417
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Kawabata T, Yamaguchi S, Buske T, Luebben SW, Wallace M, Matise I, Schimenti JC, Shima N. A reduction of licensed origins reveals strain-specific replication dynamics in mice. Mamm Genome 2011; 22:506-17. [PMID: 21611832 DOI: 10.1007/s00335-011-9333-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2011] [Accepted: 05/04/2011] [Indexed: 12/24/2022]
Abstract
Replication origin licensing builds a fundamental basis for DNA replication in all eukaryotes. This occurs during the late M to early G1 phases in which chromatin is licensed by loading of the MCM2-7 complex, an essential component of the replicative helicase. In the following S phase, only a minor fraction of chromatin-bound MCM2-7 complexes are activated to unwind the DNA. Therefore, it is proposed that the vast majority of MCM2-7 complexes license dormant origins that can be used as backups. Consistent with this idea, it has been repeatedly demonstrated that a reduction (~60%) in chromatin-bound MCM2-7 complexes has little effect on the density of active origins. In this study, however, we describe the first exception to this observation. A reduction of licensed origins due to Mcm4 ( chaos3 ) homozygosity reduces active origin density in primary embryonic fibroblasts (MEFs) in a C57BL/6J (B6) background. We found that this is associated with an intrinsically lower level of active origins in this background compared to others. B6 Mcm4 ( chaos3/chaos3 ) cells proliferate slowly due to p53-dependent upregulation of p21. In fact, the development of B6 Mcm4 ( chaos3/chaos3 ) mice is impaired and a significant fraction of them die at birth. While inactivation of p53 restores proliferation in B6 Mcm4 ( chaos3/chaos3 ) MEFs, it paradoxically does not rescue animal lethality. These findings indicate that a reduction of licensed origins may cause a more profound effect on cell types with lower densities of active origins. Moreover, p53 is required for the development of mice that suffer from intrinsic replication stress.
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Affiliation(s)
- Tsuyoshi Kawabata
- Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, MN 55455, USA.
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418
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Abstract
Claspin is a mediator of the ATR-dependent DNA replication checkpoint in human cells and also promotes DNA replication fork progression and stability. Though Claspin has been shown to bind DNA and co-immunoprecipitate with other replication fork-associated proteins, the specific protein-protein and protein-DNA interactions that are important for Claspin function are not known. We therefore purified several domains of human Claspin and then tested for direct interactions of these fragments with several replication fork-associated proteins and with DNA. Our data show that the N terminus of Claspin binds to the replicative helicase co-factor Cdc45, the Timeless protein and a branched, replication fork-like DNA structure. In contrast, the C terminus of Claspin associates with DNA polymerase epsilon and Rad17-Replication Factor C (RFC). We conclude that multiple protein-DNA and protein-protein interactions may be important for Claspin function during DNA replication and DNA replication checkpoint signaling.
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Affiliation(s)
- Ozdemirhan Serçin
- University of North Carolina School of Medicine, Chapel Hill, NC USA
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419
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Borowiec JA, Schildkraut CL. Open sesame: activating dormant replication origins in the mouse immunoglobulin heavy chain (Igh) locus. Curr Opin Cell Biol 2011; 23:284-92. [PMID: 21571518 DOI: 10.1016/j.ceb.2011.04.004] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2011] [Revised: 04/12/2011] [Accepted: 04/13/2011] [Indexed: 11/16/2022]
Abstract
Chromosomal DNA replication in mammals initiates from replication origins whose activity differs in accordance with cell type and differentiation state. In addition to origins that are active in unperturbed conditions, chromosomes also contain dormant origins that can become functional in response to certain genotoxic stress conditions. Improper regulation of origin usage can cause genomic instability leading to tumorigenesis. We review findings from recent single-molecule DNA fiber studies examining replication of the mouse immunoglobulin heavy chain (Igh) locus, in which origin activity over a 400kb region is subject to dramatic developmental regulation. Possible models are discussed to explain such differential origin usage, particularly during replication stress conditions that can activate dormant origins.
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Affiliation(s)
- James A Borowiec
- Department of Biochemistry and New York University Cancer Institute, New York University School of Medicine, New York, NY 10016, United States
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420
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Oyama T, Ishino S, Fujino S, Ogino H, Shirai T, Mayanagi K, Saito M, Nagasawa N, Ishino Y, Morikawa K. Architectures of archaeal GINS complexes, essential DNA replication initiation factors. BMC Biol 2011; 9:28. [PMID: 21527023 PMCID: PMC3114041 DOI: 10.1186/1741-7007-9-28] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2011] [Accepted: 04/28/2011] [Indexed: 11/10/2022] Open
Abstract
Background In the early stage of eukaryotic DNA replication, the template DNA is unwound by the MCM helicase, which is activated by forming a complex with the Cdc45 and GINS proteins. The eukaryotic GINS forms a heterotetramer, comprising four types of subunits. On the other hand, the archaeal GINS appears to be either a tetramer formed by two types of subunits in a 2:2 ratio (α2β2) or a homotetramer of a single subunit (α4). Due to the low sequence similarity between the archaeal and eukaryotic GINS subunits, the atomic structures of the archaeal GINS complexes are attracting interest for comparisons of their subunit architectures and organization. Results We determined the crystal structure of the α2β2 GINS tetramer from Thermococcus kodakaraensis (TkoGINS), comprising Gins51 and Gins23, and compared it with the reported human GINS structures. The backbone structure of each subunit and the tetrameric assembly are similar to those of human GINS. However, the location of the C-terminal small domain of Gins51 is remarkably different between the archaeal and human GINS structures. In addition, TkoGINS exhibits different subunit contacts from those in human GINS, as a consequence of the different relative locations and orientations between the domains. Based on the GINS crystal structures, we built a homology model of the putative homotetrameric GINS from Thermoplasma acidophilum (TacGINS). Importantly, we propose that a long insertion loop allows the differential positioning of the C-terminal domains and, as a consequence, exclusively leads to the formation of an asymmetric homotetramer rather than a symmetrical one. Conclusions The DNA metabolizing proteins from archaea are similar to those from eukaryotes, and the archaeal multi-subunit complexes are occasionally simplified versions of the eukaryotic ones. The overall similarity in the architectures between the archaeal and eukaryotic GINS complexes suggests that the GINS function, directed through interactions with other protein components, is basically conserved. On the other hand, the different subunit contacts, including the locations and contributions of the C-terminal domains to the tetramer formation, imply the possibility that the archaeal and eukaryotic GINS complexes contribute to DNA unwinding reactions by significantly different mechanisms in terms of the atomic details.
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Affiliation(s)
- Takuji Oyama
- Laboratory of Protein Organic Chemistry, Institute for Protein Research, Osaka University, Open Laboratories of Advanced Bioscience and Biotechnology (OLABB), Osaka 565-0874, Japan.
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421
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Abstract
Most of the core components of the archaeal chromosomal DNA replication apparatus share significant protein sequence similarity with eukaryotic replication factors, making the Archaea an excellent model system for understanding the biology of chromosome replication in eukaryotes. The present review summarizes current knowledge of how the core components of the archaeal chromosome replication apparatus interact with one another to perform their essential functions.
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422
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Sld7, an Sld3-associated protein required for efficient chromosomal DNA replication in budding yeast. EMBO J 2011; 30:2019-30. [PMID: 21487389 DOI: 10.1038/emboj.2011.115] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2010] [Accepted: 03/23/2011] [Indexed: 01/16/2023] Open
Abstract
Genetic screening of yeast for sld (synthetic lethality with dpb11) mutations has identified replication proteins, including Sld2, -3, and -5, and clarified the molecular mechanisms underlying eukaryotic chromosomal DNA replication. Here, we report a new replication protein, Sld7, identified by rescreening of sld mutations. Throughout the cell cycle, Sld7 forms a complex with Sld3, which associates with replication origins in a complex with Cdc45, binds to Dpb11 when phosphorylated by cyclin-dependent kinase, and dissociates from origins once DNA replication starts. However, Sld7 does not move with the replication fork. Sld7 binds to the nonessential N-terminal portion of Sld3 and reduces its affinity for Cdc45, a component of the replication fork. Although Sld7 is not essential for cell growth, its absence reduces the level of cellular Sld3, delays the dissociation from origins of GINS, a component of the replication fork, and slows S-phase progression. These results suggest that Sld7 is required for the proper function of Sld3 at the initiation of DNA replication.
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423
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Lyubimov AY, Strycharska M, Berger JM. The nuts and bolts of ring-translocase structure and mechanism. Curr Opin Struct Biol 2011; 21:240-8. [PMID: 21282052 PMCID: PMC3070846 DOI: 10.1016/j.sbi.2011.01.002] [Citation(s) in RCA: 98] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2010] [Revised: 12/30/2010] [Accepted: 01/03/2011] [Indexed: 01/27/2023]
Abstract
Ring-shaped, oligomeric translocases are multisubunit enzymes that couple the hydrolysis of Nucleoside TriPhosphates (NTPs) to directed movement along extended biopolymer substrates. These motors help unwind nucleic acid duplexes, unfold protein chains, and shepherd nucleic acids between cellular and/or viral compartments. Substrates are translocated through a central pore formed by a circular array of catalytic subunits. Cycles of nucleotide binding, hydrolysis, and product release help reposition translocation loops in the pore to direct movement. How NTP turnover allosterically induces these conformational changes, and the extent of mechanistic divergence between motor families, remain outstanding problems. This review examines the current models for ring-translocase function and highlights the fundamental gaps remaining in our understanding of these molecular machines.
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Affiliation(s)
- Artem Y Lyubimov
- Department of Molecular and Cell Biology, University of California, Berkeley, 360 Stanley Hall, Berkeley, CA, USA
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424
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Costa A, Ilves I, Tamberg N, Petojevic T, Nogales E, Botchan MR, Berger JM. The structural basis for MCM2-7 helicase activation by GINS and Cdc45. Nat Struct Mol Biol 2011; 18:471-7. [PMID: 21378962 PMCID: PMC4184033 DOI: 10.1038/nsmb.2004] [Citation(s) in RCA: 263] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2010] [Accepted: 12/09/2010] [Indexed: 11/09/2022]
Abstract
Two central steps for initiating eukaryotic DNA replication involve loading of the Mcm2-7 helicase onto double-stranded DNA and its activation by GINS-Cdc45. To better understand these events, we determined the structures of Mcm2-7 and the CMG complex by using single-particle electron microscopy. Mcm2-7 adopts two conformations--a lock-washer-shaped spiral state and a planar, gapped-ring form--in which Mcm2 and Mcm5 flank a breach in the helicase perimeter. GINS and Cdc45 bridge this gap, forming a topologically closed assembly with a large interior channel; nucleotide binding further seals off the discontinuity between Mcm2 and Mcm5, partitioning the channel into two smaller pores. Together, our data help explain how GINS and Cdc45 activate Mcm2-7, indicate that Mcm2-7 loading may be assisted by a natural predisposition of the hexamer to form open rings, and suggest a mechanism by which the CMG complex assists DNA strand separation.
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Affiliation(s)
- Alessandro Costa
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California, USA
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425
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Gambus A, Khoudoli GA, Jones RC, Blow JJ. MCM2-7 form double hexamers at licensed origins in Xenopus egg extract. J Biol Chem 2011; 286:11855-64. [PMID: 21282109 PMCID: PMC3064236 DOI: 10.1074/jbc.m110.199521] [Citation(s) in RCA: 107] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2010] [Revised: 01/06/2011] [Indexed: 02/01/2023] Open
Abstract
In late mitosis and G1, Mcm2-7 are assembled onto replication origins to license them for initiation in the upcoming S phase. After initiation, Mcm2-7 provide helicase activity to unwind DNA at the replication fork. Here we examine the structure of Mcm2-7 on chromatin in Xenopus egg extracts. We show that prior to replication initiation, Mcm2-7 is present at licensed replication origins in a complex with a molecular mass close to double that of the Mcm2-7 hexamer. This complex has approximately stoichiometric quantities of the 6 Mcm2-7 proteins and we conclude that it consists of a double heterohexamer. This provides a configuration potentially capable of initiating a pair of bidirectional replication forks in S phase. We also show that after initiation, Mcm2-7 associate with Cdc45 and GINS to form a relatively stable CMG (Cdc45-MCM-GINS) complex. The CMG proteins also associate less strongly with other replication proteins, consistent with the idea that a single CMG complex forms the core of the replisome.
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Affiliation(s)
- Agnieszka Gambus
- From the Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee DD1 5EH, United Kingdom and
| | - Guennadi A. Khoudoli
- From the Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee DD1 5EH, United Kingdom and
| | | | - J. Julian Blow
- From the Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee DD1 5EH, United Kingdom and
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426
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Kawabata T, Luebben SW, Yamaguchi S, Ilves I, Matise I, Buske T, Botchan MR, Shima N. Stalled fork rescue via dormant replication origins in unchallenged S phase promotes proper chromosome segregation and tumor suppression. Mol Cell 2011; 41:543-53. [PMID: 21362550 PMCID: PMC3062258 DOI: 10.1016/j.molcel.2011.02.006] [Citation(s) in RCA: 169] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2010] [Revised: 11/24/2010] [Accepted: 12/21/2010] [Indexed: 01/25/2023]
Abstract
Eukaryotic cells license far more origins than are actually used for DNA replication, thereby generating a large number of dormant origins. Accumulating evidence suggests that such origins play a role in chromosome stability and tumor suppression, though the underlying mechanism is largely unknown. Here, we show that a loss of dormant origins results in an increased number of stalled replication forks, even in unchallenged S phase in primary mouse fibroblasts derived from embryos homozygous for the Mcm4(Chaos3) allele. We found that this allele reduces the stability of the MCM2-7 complex, but confers normal helicase activity in vitro. Despite the activation of multiple fork recovery pathways, replication intermediates in these cells persist into M phase, increasing the number of abnormal anaphase cells with lagging chromosomes and/or acentric fragments. These findings suggest that dormant origins constitute a major pathway for stalled fork recovery, contributing to faithful chromosome segregation and tumor suppression.
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Affiliation(s)
- Tsuyoshi Kawabata
- Department of Genetics, Cell Biology and Development, University of Minnesota
- Masonic Cancer Center, Minneapolis, MN 55455 USA
| | - Spencer W. Luebben
- Department of Genetics, Cell Biology and Development, University of Minnesota
| | - Satoru Yamaguchi
- Department of Genetics, Cell Biology and Development, University of Minnesota
- Masonic Cancer Center, Minneapolis, MN 55455 USA
| | - Ivar Ilves
- Department of Molecular and Cell Biology, Division of Biochemistry and Molecular Biology, University of California, Berkeley, Berkeley, CA 94720 USA
| | - Ilze Matise
- Masonic Cancer Center, Minneapolis, MN 55455 USA
- College of Veterinary Medicine, University of Minnesota, St. Paul, MN 55108 USA
| | - Tavanna Buske
- Department of Genetics, Cell Biology and Development, University of Minnesota
| | - Michael R. Botchan
- Department of Molecular and Cell Biology, Division of Biochemistry and Molecular Biology, University of California, Berkeley, Berkeley, CA 94720 USA
| | - Naoko Shima
- Department of Genetics, Cell Biology and Development, University of Minnesota
- Masonic Cancer Center, Minneapolis, MN 55455 USA
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427
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Bruck I, Kaplan DL. GINS and Sld3 compete with one another for Mcm2-7 and Cdc45 binding. J Biol Chem 2011; 286:14157-67. [PMID: 21362622 DOI: 10.1074/jbc.m111.218305] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Sld3 is essential for the initiation of DNA replication, but Sld3 does not travel with a replication fork. GINS binds to Cdc45 and Mcm2-7 to form the replication fork helicase in eukaryotes. We purified Sld3, Cdc45, GINS, and Mcm2-7 and studied their interaction and assembly into complexes. Sld3 binds tightly to Cdc45 in the presence or absence of cyclin-dependent kinase activity. Furthermore, Sld3 binds tightly to the Mcm2-7 complex, and a ternary complex forms among Cdc45, Mcm2-7, and Sld3, with a 1:1:1 stoichiometry (CMS complex). GINS binds directly to Mcm2-7, and GINS competes with Sld3 for Mcm2-7 binding. GINS also binds directly to Cdc45, and GINS competes with Sld3 for Cdc45 binding. Cdc45, Mcm2-7, and GINS form a ternary complex with a stoichiometry of 1:1:1 (CMG complex). Size exclusion data reveal that when Sld3, Cdc45, Mcm2-7, and GINS are added together, the result is a mixture of CMS and CMG complexes. The data suggest that GINS and Sld3 compete with one another for Mcm2-7 and Cdc45 binding. Our results are consistent with a model wherein GINS trades places with Sld3 at a replication origin, contributing to the activation of the replication fork helicase.
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Affiliation(s)
- Irina Bruck
- Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee 37235, USA
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428
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Kuipers MA, Stasevich TJ, Sasaki T, Wilson KA, Hazelwood KL, McNally JG, Davidson MW, Gilbert DM. Highly stable loading of Mcm proteins onto chromatin in living cells requires replication to unload. ACTA ACUST UNITED AC 2011; 192:29-41. [PMID: 21220507 PMCID: PMC3019549 DOI: 10.1083/jcb.201007111] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Components of the minichromosome maintenance complex (Mcm2-7) remain indefinitely bound to chromatin during G1 phase and replication arrest. The heterohexameric minichromosome maintenance protein complex (Mcm2-7) functions as the eukaryotic helicase during DNA replication. Mcm2-7 loads onto chromatin during early G1 phase but is not converted into an active helicase until much later during S phase. Hence, inactive Mcm complexes are presumed to remain stably bound from early G1 through the completion of S phase. Here, we investigated Mcm protein dynamics in live mammalian cells. We demonstrate that Mcm proteins are irreversibly loaded onto chromatin cumulatively throughout G1 phase, showing no detectable exchange with a gradually diminishing soluble pool. Eviction of Mcm requires replication; during replication arrest, Mcm proteins remained bound indefinitely. Moreover, the density of immobile Mcms is reduced together with chromatin decondensation within sites of active replication, which provides an explanation for the lack of colocalization of Mcm with replication fork proteins. These results provide in vivo evidence for an exceptionally stable lockdown mechanism to retain all loaded Mcm proteins on chromatin throughout prolonged cell cycles.
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Affiliation(s)
- Marjorie A Kuipers
- Department of Biological Science, Florida State University, Tallahassee, FL 32306, USA
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429
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Abstract
The copying of chromosomal DNA initiates from a single nucleoprotein assembly called the prereplication complex. New findings in a recent issue of Molecular Cell (Yardimci et al., 2010) reveal that this complex dissolves into two independent replisomes that move away from each other as DNA synthesis ensues.
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Affiliation(s)
- Michael Botchan
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA.
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430
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Sherwood R, Takahashi TS, Jallepalli PV. Sister acts: coordinating DNA replication and cohesion establishment. Genes Dev 2010; 24:2723-31. [PMID: 21159813 PMCID: PMC3003188 DOI: 10.1101/gad.1976710] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The ring-shaped cohesin complex links sister chromatids and plays crucial roles in homologous recombination and mitotic chromosome segregation. In cycling cells, cohesin's ability to generate cohesive linkages is restricted to S phase and depends on loading and establishment factors that are intimately connected to DNA replication. Here we review how cohesin is regulated by the replication machinery, as well as recent evidence that cohesin itself influences how chromosomes are replicated.
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Affiliation(s)
- Rebecca Sherwood
- Molecular Biology Program, Memorial Sloan-Kettering Cancer Center, New York, New York 10065, USA
| | - Tatsuro S. Takahashi
- Department of Biological Science, Graduate School of Science, Osaka University, Toyonaka Osaka 560-0043, Japan
| | - Prasad V. Jallepalli
- Molecular Biology Program, Memorial Sloan-Kettering Cancer Center, New York, New York 10065, USA
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431
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Yardimci H, Loveland AB, Habuchi S, van Oijen AM, Walter JC. Uncoupling of sister replisomes during eukaryotic DNA replication. Mol Cell 2010; 40:834-40. [PMID: 21145490 PMCID: PMC3004751 DOI: 10.1016/j.molcel.2010.11.027] [Citation(s) in RCA: 101] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2010] [Revised: 09/13/2010] [Accepted: 09/24/2010] [Indexed: 01/19/2023]
Abstract
The duplication of eukaryotic genomes involves the replication of DNA from multiple origins of replication. In S phase, two sister replisomes assemble at each active origin, and they replicate DNA in opposite directions. Little is known about the functional relationship between sister replisomes. Some data imply that they travel away from one another and thus function independently. Alternatively, sister replisomes may form a stationary, functional unit that draws parental DNA toward itself. If this "double replisome" model is correct, a constrained DNA molecule should not undergo replication. To test this prediction, lambda DNA was stretched and immobilized at both ends within a microfluidic flow cell. Upon exposure to Xenopus egg extracts, this DNA underwent extensive replication by a single pair of diverging replisomes. The data show that there is no obligatory coupling between sister replisomes and, together with other studies, imply that genome duplication involves autonomously functioning replisomes.
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Affiliation(s)
- Hasan Yardimci
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA , USA
| | - Anna B. Loveland
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA , USA
| | - Satoshi Habuchi
- Graduate School of Science and Engineering, Tokyo Institute of Technology, Tokyo, Japan
| | - Antoine M. van Oijen
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA , USA
| | - Johannes C. Walter
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA , USA
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432
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Randell JCW, Fan A, Chan C, Francis LI, Heller RC, Galani K, Bell SP. Mec1 is one of multiple kinases that prime the Mcm2-7 helicase for phosphorylation by Cdc7. Mol Cell 2010; 40:353-63. [PMID: 21070963 PMCID: PMC3021128 DOI: 10.1016/j.molcel.2010.10.017] [Citation(s) in RCA: 135] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2010] [Revised: 07/27/2010] [Accepted: 08/24/2010] [Indexed: 01/18/2023]
Abstract
Activation of the eukaryotic replicative DNA helicase, the Mcm2-7 complex, requires phosphorylation by Cdc7/Dbf4 (Dbf4-dependent kinase or DDK), which, in turn, depends on prior phosphorylation of Mcm2-7 by an unknown kinase (or kinases). We identified DDK phosphorylation sites on Mcm4 and Mcm6 and found that phosphorylation of either subunit suffices for cell proliferation. Importantly, prior phosphorylation of either S/T-P or S/T-Q motifs on these subunits is required for DDK phosphorylation of Mcm2-7 and for normal S phase passage. Phosphomimetic mutations of DDK target sites bypass both DDK function and mutation of the priming phosphorylation sites. Mrc1 facilitates Mec1 phosphorylation of the S/T-Q motifs of chromatin-bound Mcm2-7 during S phase to activate replication. Genetic interactions between priming site mutations and MRC1 or TOF1 deletion support a role for these modifications in replication fork stability. These findings identify regulatory mechanisms that modulate origin firing and replication fork assembly during cell cycle progression.
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Affiliation(s)
- John C. W. Randell
- Howard Hughes Medical Institute Department of Biology Massachusetts Institute of Technology Cambridge, MA 02139
| | | | | | | | - Ryan C. Heller
- Howard Hughes Medical Institute Department of Biology Massachusetts Institute of Technology Cambridge, MA 02139
| | - Kyriaki Galani
- Howard Hughes Medical Institute Department of Biology Massachusetts Institute of Technology Cambridge, MA 02139
| | - Stephen P. Bell
- Howard Hughes Medical Institute Department of Biology Massachusetts Institute of Technology Cambridge, MA 02139
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433
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Huang H, Zhao K, Arnett DR, Fanning E. A specific docking site for DNA polymerase {alpha}-primase on the SV40 helicase is required for viral primosome activity, but helicase activity is dispensable. J Biol Chem 2010; 285:33475-33484. [PMID: 20685648 PMCID: PMC2963361 DOI: 10.1074/jbc.m110.156240] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2010] [Revised: 07/31/2010] [Indexed: 11/06/2022] Open
Abstract
Replication of simian virus 40 (SV40) DNA, a model for eukaryotic chromosomal replication, can be reconstituted in vitro using the viral helicase (large tumor antigen, or Tag) and purified human proteins. Tag interacts physically with two cellular proteins, replication protein A and DNA polymerase α-primase (pol-prim), constituting the viral primosome. Like the well characterized primosomes of phages T7 and T4, this trio of proteins coordinates parental DNA unwinding with primer synthesis to initiate the leading strand at the viral origin and each Okazaki fragment on the lagging strand template. We recently determined the structure of a previously unrecognized pol-prim domain (p68N) that docks on Tag, identified the p68N surface that contacts Tag, and demonstrated its vital role in primosome function. Here, we identify the p68N-docking site on Tag by using structure-guided mutagenesis of the Tag helicase surface. A charge reverse substitution in Tag disrupted both p68N-binding and primosome activity but did not affect docking with other pol-prim subunits. Unexpectedly, the substitution also disrupted Tag ATPase and helicase activity, suggesting a potential link between p68N docking and ATPase activity. To assess this possibility, we examined the primosome activity of Tag with a single residue substitution in the Walker B motif. Although this substitution abolished ATPase and helicase activity as expected, it did not reduce pol-prim docking on Tag or primosome activity on single-stranded DNA, indicating that Tag ATPase is dispensable for primosome activity in vitro.
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Affiliation(s)
- Hao Huang
- From the Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee 37235-1634
| | - Kun Zhao
- From the Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee 37235-1634
| | - Diana R Arnett
- From the Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee 37235-1634
| | - Ellen Fanning
- From the Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee 37235-1634.
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434
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Eukaryotic DNA replication origins: many choices for appropriate answers. Nat Rev Mol Cell Biol 2010; 11:728-38. [DOI: 10.1038/nrm2976] [Citation(s) in RCA: 314] [Impact Index Per Article: 20.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
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435
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The effects of oligomerization on Saccharomyces cerevisiae Mcm4/6/7 function. BMC BIOCHEMISTRY 2010; 11:37. [PMID: 20860810 PMCID: PMC2949612 DOI: 10.1186/1471-2091-11-37] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/30/2010] [Accepted: 09/22/2010] [Indexed: 12/29/2022]
Abstract
BACKGROUND Minichromosome maintenance proteins (Mcm) 2, 3, 4, 5, 6 and 7 are related by sequence and form a variety of complexes that unwind DNA, including Mcm4/6/7. A Mcm4/6/7 trimer forms one half of the Mcm2-7 hexameric ring and can be thought of as the catalytic core of Mcm2-7, the replicative helicase in eukaryotic cells. Oligomeric analysis of Mcm4/6/7 suggests that it forms a hexamer containing two Mcm4/6/7 trimers, however, under certain conditions trimeric Mcm4/6/7 has also been observed. The functional significance of the different Mcm4/6/7 oligomeric states has not been assessed. The results of such an assessment would have implications for studies of both Mcm4/6/7 and Mcm2-7. RESULTS Here, we show that Saccharomyces cerevisiae Mcm4/6/7 reconstituted from individual subunits exists in an equilibrium of oligomeric forms in which smaller oligomers predominate in the absence of ATP. In addition, we found that ATP, which is required for Mcm4/6/7 activity, shifts the equilibrium towards larger oligomers, likely hexamers of Mcm4/6/7. ATPγS and to a lesser extent ADP also shift the equilibrium towards hexamers. Study of Mcm4/6/7 complexes containing mutations that interfere with the formation of inter-subunit ATP sites (arginine finger mutants) indicates that full activity of Mcm4/6/7 requires all of its ATP sites, which are formed in a hexamer and not a trimer. In keeping with this observation, Mcm4/6/7 binds DNA as a hexamer. CONCLUSIONS The minimal functional unit of Mcm4/6/7 is a hexamer. One of the roles of ATP binding by Mcm4/6/7 may be to stabilize formation of hexamers.
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436
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Harrison MM, Botchan MR, Cline TW. Grainyhead and Zelda compete for binding to the promoters of the earliest-expressed Drosophila genes. Dev Biol 2010; 345:248-55. [PMID: 20599892 PMCID: PMC2927720 DOI: 10.1016/j.ydbio.2010.06.026] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2010] [Revised: 05/24/2010] [Accepted: 06/17/2010] [Indexed: 10/19/2022]
Abstract
Maternally contributed mRNAs and proteins control the initial stages of development following fertilization. During this time, most of the zygotic genome remains transcriptionally silent. The initiation of widespread zygotic transcription is coordinated with the degradation of maternally provided mRNAs at the maternal-to-zygotic transition (MZT). While most of the genome is silenced prior to the MZT, a small subset of zygotic genes essential for the future development of the organism is transcribed. Previous work in our laboratory and others identified the TAGteam element, a set of related heptameric DNA-sequences in the promoters of many early-expressed Drosophila genes required to drive their unusually early transcription. To understand how this unique subset of genes is regulated, we identified a TAGteam-binding factor Grainyhead (Grh). We demonstrated that Grh and the previously characterized transcriptional activator Zelda (Zld) bind to different TAGteam sequences with varying affinities, and that Grh competes with Zld for TAGteam occupancy. Moreover, overexpression of Grh in the early embryo causes defects in cell division, phenocopying Zld depletion. Our findings indicate that during early embryonic development the precise timing of gene expression is regulated by both the sequence of the TAGteam elements in the promoter and the relative levels of the transcription factors Grh and Zld.
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Affiliation(s)
- Melissa M Harrison
- Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA.
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437
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Gouge CA, Christensen TW. Drosophila Sld5 is essential for normal cell cycle progression and maintenance of genomic integrity. Biochem Biophys Res Commun 2010; 400:145-50. [PMID: 20709026 PMCID: PMC2939264 DOI: 10.1016/j.bbrc.2010.08.033] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2010] [Accepted: 08/09/2010] [Indexed: 10/19/2022]
Abstract
Essential for the normal functioning of a cell is the maintenance of genomic integrity. Failure in this process is often catastrophic for the organism, leading to cell death or mis-proliferation. Central to genomic integrity is the faithful replication of DNA during S phase. The GINS complex has recently come to light as a critical player in DNA replication through stabilization of MCM2-7 and Cdc45 as a member of the CMG complex which is likely responsible for the processivity of helicase activity during S phase. The GINS complex is made up of 4 members in a 1:1:1:1 ratio: Psf1, Psf2, Psf3, And Sld5. Here we present the first analysis of the function of the Sld5 subunit in a multicellular organism. We show that Drosophila Sld5 interacts with Psf1, Psf2, and Mcm10 and that mutations in Sld5 lead to M and S phase delays with chromosomes exhibiting hallmarks of genomic instability.
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Affiliation(s)
- Catherine A. Gouge
- East Carolina University Department of Biology, East Carolina University, Greenville, NC 27858
| | - Tim W. Christensen
- East Carolina University Department of Biology, East Carolina University, Greenville, NC 27858
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438
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Masai H, Matsumoto S, You Z, Yoshizawa-Sugata N, Oda M. Eukaryotic chromosome DNA replication: where, when, and how? Annu Rev Biochem 2010; 79:89-130. [PMID: 20373915 DOI: 10.1146/annurev.biochem.052308.103205] [Citation(s) in RCA: 385] [Impact Index Per Article: 25.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
DNA replication is central to cell proliferation. Studies in the past six decades since the proposal of a semiconservative mode of DNA replication have confirmed the high degree of conservation of the basic machinery of DNA replication from prokaryotes to eukaryotes. However, the need for replication of a substantially longer segment of DNA in coordination with various internal and external signals in eukaryotic cells has led to more complex and versatile regulatory strategies. The replication program in higher eukaryotes is under a dynamic and plastic regulation within a single cell, or within the cell population, or during development. We review here various regulatory mechanisms that control the replication program in eukaryotes and discuss future directions in this dynamic field.
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Affiliation(s)
- Hisao Masai
- Genome Dynamics Project, Tokyo Metropolitan Institute of Medical Science, Tokyo 156-8506, Japan.
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439
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Bochman ML, Schwacha A. The Saccharomyces cerevisiae Mcm6/2 and Mcm5/3 ATPase active sites contribute to the function of the putative Mcm2-7 'gate'. Nucleic Acids Res 2010; 38:6078-88. [PMID: 20484375 PMCID: PMC2952866 DOI: 10.1093/nar/gkq422] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The Mcm2-7 complex is the eukaryotic replicative helicase, a toroidal AAA+ molecular motor that uses adenosine triphosphate (ATP) binding and hydrolysis to separate duplex DNA strands during replication. This heterohexameric helicase contains six different and essential subunits (Mcm2 through Mcm7), with the corresponding dimer interfaces forming ATPase active sites from conserved motifs of adjacent subunits. As all other known hexameric helicases are formed from six identical subunits, the function of the unique heterohexameric organization of Mcm2-7 is of particular interest. Indeed, prior work using mutations in the conserved Walker A box ATPase structural motif strongly suggests that individual ATPase active sites contribute differentially to Mcm2-7 activity. Although only a specific subset of active sites is required for helicase activity, another ATPase active site (Mcm2/5) may serve as a reversible ATP-dependent discontinuity (‘gate’) within the hexameric ring structure. This study analyzes the contribution that two other structural motifs, the Walker B box and arginine finger, make to each Mcm2-7 ATPase active site. Mutational analysis of these motifs not only confirms that Mcm ATPase active sites contribute unequally to activity but implicates the involvement of at least two additional active sites (Mcm5/3 and 6/2) in modulating the activity of the putative Mcm2/5 gate.
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Affiliation(s)
- Matthew L Bochman
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260, USA
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440
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Robertson PD, Chagot B, Chazin WJ, Eichman BF. Solution NMR structure of the C-terminal DNA binding domain of Mcm10 reveals a conserved MCM motif. J Biol Chem 2010; 285:22942-9. [PMID: 20489205 DOI: 10.1074/jbc.m110.131276] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The eukaryotic DNA replication protein Mcm10 associates with chromatin in early S-phase and is required for assembly and function of the replication fork protein machinery. Xenopus laevis (X) Mcm10 binds DNA via a highly conserved internal domain (ID) and a C-terminal domain (CTD) that is unique to higher eukaryotes. Although the structural basis of the interactions of the ID with DNA and polymerase alpha is known, little information is available for the CTD. We have identified the minimal DNA binding region of the XMcm10-CTD and determined its three-dimensional structure by solution NMR. The CTD contains a globular domain composed of two zinc binding motifs. NMR chemical shift perturbation and mutational analysis show that ssDNA binds only to the N-terminal (CCCH-type) zinc motif, whose structure is unique to Mcm10. The second (CCCC-type) zinc motif is not involved in DNA binding. However, it is structurally similar to the CCCC zinc ribbon in the N-terminal oligomerization domain of eukaryotic and archaeal MCM helicases. NMR analysis of a construct spanning both the ID and CTD reveals that the two DNA binding domains are structurally independent in solution, supporting a modular architecture for vertebrate Mcm10. Our results provide insight in the action of Mcm10 in the replisome and support a model in which it serves as a central scaffold through coupling of interactions with partner proteins and the DNA.
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Affiliation(s)
- Patrick D Robertson
- Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee 37232, USA
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441
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Muramatsu S, Hirai K, Tak YS, Kamimura Y, Araki H. CDK-dependent complex formation between replication proteins Dpb11, Sld2, Pol (epsilon}, and GINS in budding yeast. Genes Dev 2010; 24:602-12. [PMID: 20231317 DOI: 10.1101/gad.1883410] [Citation(s) in RCA: 200] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Eukaryotic chromosomal DNA replication requires cyclin-dependent kinase (CDK) activity. CDK phosphorylates two yeast replication proteins, Sld3 and Sld2, both of which bind to Dpb11 when phosphorylated. These phosphorylation-dependent interactions are essential and are the minimal requirements for CDK-dependent activation of DNA replication. However, how these interactions activate DNA replication has not been elucidated. Here, we show that CDK promotes the formation of a newly identified fragile complex, the preloading complex (pre-LC) containing DNA polymerase epsilon (Pol epsilon), GINS, Sld2, and Dpb11. Formation of the pre-LC requires phosphorylation of Sld2 by CDK, but is independent of DNA replication, protein association with replication origins, and Dbf4-dependent Cdc7 kinase, which is also essential for the activation of DNA replication. We also demonstrate that Pol epsilon, GINS, Dpb11, and CDK-phosphorylated Sld2 form a complex in vitro. The genetic interactions between Pol epsilon, GINS, Sld2, and Dpb11 suggest further that they form an essential complex in cells. We propose that CDK regulates the initiation of DNA replication in budding yeast through formation of the pre-LC.
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