1
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Cebrián J, Martínez V, Hernández P, Krimer DB, Martínez-Robles ML, Schvartzman JB, Fernández-Nestosa MJ. Electrophoretic Mobility Assay to Separate Supercoiled, Catenated, and Knotted DNA Molecules. Bio Protoc 2024; 14:e4983. [PMID: 38737504 PMCID: PMC11082789 DOI: 10.21769/bioprotoc.4983] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2023] [Revised: 04/10/2024] [Accepted: 04/12/2024] [Indexed: 05/14/2024] Open
Abstract
Two-dimensional (2D) agarose gel electrophoresis is the method of choice to analyze DNA topology. The possibility to use E. coli strains with different genetic backgrounds in combination with nicking enzymes and different concentrations of norfloxacin improves the resolution of 2D gels to study the electrophoretic behavior of three different families of DNA topoisomers: supercoiled DNA molecules, post-replicative catenanes, and knotted DNA molecules. Here, we describe the materials and procedures required to optimize their separation by 2D gels. Understanding the differences in their electrophoretic behavior can help explain some important physical characteristics of these different types of DNA topoisomers. Key features • Preparative method to enrich DNA samples of supercoiled, catenated, and knotted families of topoisomers, later analyzed by 2D gels (or other techniques, e.g., microscopy). • 2D gels facilitate the separation of the topoisomers of any given circular DNA molecule. • Separation of DNA molecules with the same molecular masses but different shapes can be optimized by modifying the conditions of 2D gels. • Evaluating the roles of electric field and agarose concentration on the electrophoretic mobility of DNA topoisomers sheds light on their physical characteristics.
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Affiliation(s)
- Jorge Cebrián
- Department of Cellular and Molecular Biology, Margarita Salas Center for Biological Research (CSIC), Madrid, Spain
| | - Victor Martínez
- Polytechnic School, National University of Asuncion, San Lorenzo, Paraguay
| | - Pablo Hernández
- Department of Cellular and Molecular Biology, Margarita Salas Center for Biological Research (CSIC), Madrid, Spain
| | - Dora B. Krimer
- Department of Cellular and Molecular Biology, Margarita Salas Center for Biological Research (CSIC), Madrid, Spain
| | - María-Luisa Martínez-Robles
- Department of Cellular and Molecular Biology, Margarita Salas Center for Biological Research (CSIC), Madrid, Spain
| | - Jorge B. Schvartzman
- Department of Cellular and Molecular Biology, Margarita Salas Center for Biological Research (CSIC), Madrid, Spain
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2
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Moeckel C, Zaravinos A, Georgakopoulos-Soares I. Strand Asymmetries Across Genomic Processes. Comput Struct Biotechnol J 2023; 21:2036-2047. [PMID: 36968020 PMCID: PMC10030826 DOI: 10.1016/j.csbj.2023.03.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2023] [Revised: 03/08/2023] [Accepted: 03/08/2023] [Indexed: 03/12/2023] Open
Abstract
Across biological systems, a number of genomic processes, including transcription, replication, DNA repair, and transcription factor binding, display intrinsic directionalities. These directionalities are reflected in the asymmetric distribution of nucleotides, motifs, genes, transposon integration sites, and other functional elements across the two complementary strands. Strand asymmetries, including GC skews and mutational biases, have shaped the nucleotide composition of diverse organisms. The investigation of strand asymmetries often serves as a method to understand underlying biological mechanisms, including protein binding preferences, transcription factor interactions, retrotransposition, DNA damage and repair preferences, transcription-replication collisions, and mutagenesis mechanisms. Research into this subject also enables the identification of functional genomic sites, such as replication origins and transcription start sites. Improvements in our ability to detect and quantify DNA strand asymmetries will provide insights into diverse functionalities of the genome, the contribution of different mutational mechanisms in germline and somatic mutagenesis, and our knowledge of genome instability and evolution, which all have significant clinical implications in human disease, including cancer. In this review, we describe key developments that have been made across the field of genomic strand asymmetries, as well as the discovery of associated mechanisms.
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Affiliation(s)
- Camille Moeckel
- Institute for Personalized Medicine, Department of Biochemistry and Molecular Biology, The Pennsylvania State University College of Medicine, Hershey, PA, USA
| | - Apostolos Zaravinos
- Department of Life Sciences, European University Cyprus, Diogenis Str., 6, Nicosia 2404, Cyprus
- Cancer Genetics, Genomics and Systems Biology laboratory, Basic and Translational Cancer Research Center (BTCRC), Nicosia 1516, Cyprus
- Corresponding author at: Department of Life Sciences, European University Cyprus, Diogenis Str., 6, Nicosia 2404, Cyprus.
| | - Ilias Georgakopoulos-Soares
- Institute for Personalized Medicine, Department of Biochemistry and Molecular Biology, The Pennsylvania State University College of Medicine, Hershey, PA, USA
- Corresponding author.
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3
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Kwan EX, Alvino GM, Lynch KL, Levan PF, Amemiya HM, Wang XS, Johnson SA, Sanchez JC, Miller MA, Croy M, Lee SB, Naushab M, Bedalov A, Cuperus JT, Brewer BJ, Queitsch C, Raghuraman MK. Ribosomal DNA replication time coordinates completion of genome replication and anaphase in yeast. Cell Rep 2023; 42:112161. [PMID: 36842087 PMCID: PMC10142053 DOI: 10.1016/j.celrep.2023.112161] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2022] [Revised: 12/19/2022] [Accepted: 02/09/2023] [Indexed: 02/27/2023] Open
Abstract
Timely completion of genome replication is a prerequisite for mitosis, genome integrity, and cell survival. A challenge to this timely completion comes from the need to replicate the hundreds of untranscribed copies of rDNA that organisms maintain in addition to the copies required for ribosome biogenesis. Replication of these rDNA arrays is relegated to late S phase despite their large size, repetitive nature, and essentiality. Here, we show that, in Saccharomyces cerevisiae, reducing the number of rDNA repeats leads to early rDNA replication, which results in delaying replication elsewhere in the genome. Moreover, cells with early-replicating rDNA arrays and delayed genome-wide replication aberrantly release the mitotic phosphatase Cdc14 from the nucleolus and enter anaphase prematurely. We propose that rDNA copy number determines the replication time of the rDNA locus and that the release of Cdc14 upon completion of rDNA replication is a signal for cell cycle progression.
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Affiliation(s)
- Elizabeth X Kwan
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA
| | - Gina M Alvino
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA
| | - Kelsey L Lynch
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA
| | - Paula F Levan
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA
| | - Haley M Amemiya
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA
| | - Xiaobin S Wang
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA
| | - Sarah A Johnson
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA
| | - Joseph C Sanchez
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA
| | - Madison A Miller
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA
| | - Mackenzie Croy
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA
| | - Seung-Been Lee
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA
| | - Maria Naushab
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA
| | - Antonio Bedalov
- Clinical Research Division, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA
| | - Josh T Cuperus
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA
| | - Bonita J Brewer
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA
| | - Christine Queitsch
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA.
| | - M K Raghuraman
- Department of Genome Sciences, University of Washington, Seattle, WA 98195, USA.
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4
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Zhu Y, Wang Y, Tao B, Han J, Chen H, Zhu Q, Huang L, He Y, Hong J, Li Y, Chen J, Huang J, Lo LJ, Peng J. Nucleolar GTPase Bms1 displaces Ttf1 from RFB-sites to balance progression of rDNA transcription and replication. J Mol Cell Biol 2021; 13:902-917. [PMID: 34791311 PMCID: PMC8800533 DOI: 10.1093/jmcb/mjab074] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2021] [Revised: 10/30/2021] [Accepted: 11/02/2021] [Indexed: 11/24/2022] Open
Abstract
18S, 5.8S, and 28S ribosomal RNAs (rRNAs) are cotranscribed as a pre-ribosomal RNA (pre-rRNA) from the rDNA by RNA polymerase I whose activity is vigorous during the S-phase, leading to a conflict with rDNA replication. This conflict is resolved partly by replication-fork-barrier (RFB)-sites sequences located downstream of the rDNA and RFB-binding proteins such as Ttf1. However, how Ttf1 is displaced from RFB-sites to allow replication fork progression remains elusive. Here, we reported that loss-of-function of Bms1l, a nucleolar GTPase, upregulates rDNA transcription, causes replication-fork stall, and arrests cell cycle at the S-to-G2 transition; however, the G1-to-S transition is constitutively active characterized by persisting DNA synthesis. Concomitantly, ubf, tif-IA, and taf1b marking rDNA transcription, Chk2, Rad51, and p53 marking DNA-damage response, and Rpa2, PCNA, Fen1, and Ttf1 marking replication fork stall are all highly elevated in bms1l mutants. We found that Bms1 interacts with Ttf1 in addition to Rc1l. Finally, we identified RFB-sites for zebrafish Ttf1 through chromatin immunoprecipitation sequencing and showed that Bms1 disassociates the Ttf1‒RFB complex with its GTPase activity. We propose that Bms1 functions to balance rDNA transcription and replication at the S-phase through interaction with Rcl1 and Ttf1, respectively. TTF1 and Bms1 together might impose an S-phase checkpoint at the rDNA loci.
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Affiliation(s)
- Yanqing Zhu
- MOE Key Laboratory for Molecular Animal Nutrition, College of Animal Sciences, Zhejiang University, Hangzhou, 310058 China
| | - Yong Wang
- Taizhou Hospital, Zhejiang University, Taizhou, 317000 China
| | - Boxiang Tao
- MOE Key Laboratory for Molecular Animal Nutrition, College of Animal Sciences, Zhejiang University, Hangzhou, 310058 China
| | - Jinhua Han
- Life Sciences Institute, Zhejiang University, Hangzhou, 310058 China
| | - Hong Chen
- MOE Key Laboratory for Molecular Animal Nutrition, College of Animal Sciences, Zhejiang University, Hangzhou, 310058 China
| | - Qinfang Zhu
- MOE Key Laboratory for Molecular Animal Nutrition, College of Animal Sciences, Zhejiang University, Hangzhou, 310058 China
| | - Ling Huang
- MOE Key Laboratory for Molecular Animal Nutrition, College of Animal Sciences, Zhejiang University, Hangzhou, 310058 China
| | - Yinan He
- MOE Key Laboratory for Molecular Animal Nutrition, College of Animal Sciences, Zhejiang University, Hangzhou, 310058 China
| | - Jian Hong
- Institute of Biotechnology, Zhejiang University, Hangzhou, 310058 China
| | - Yunqin Li
- Institute of Biotechnology, Zhejiang University, Hangzhou, 310058 China
| | - Jun Chen
- College of Life Sciences, Zhejiang University, Hangzhou, 310058 China
| | - Jun Huang
- Life Sciences Institute, Zhejiang University, Hangzhou, 310058 China
| | - Li Jan Lo
- MOE Key Laboratory for Molecular Animal Nutrition, College of Animal Sciences, Zhejiang University, Hangzhou, 310058 China
| | - Jinrong Peng
- MOE Key Laboratory for Molecular Animal Nutrition, College of Animal Sciences, Zhejiang University, Hangzhou, 310058 China
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5
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Antagonising Chromatin Remodelling Activities in the Regulation of Mammalian Ribosomal Transcription. Genes (Basel) 2021; 12:genes12070961. [PMID: 34202617 PMCID: PMC8303148 DOI: 10.3390/genes12070961] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2021] [Revised: 06/16/2021] [Accepted: 06/19/2021] [Indexed: 12/29/2022] Open
Abstract
Ribosomal transcription constitutes the major energy consuming process in cells and is regulated in response to proliferation, differentiation and metabolic conditions by several signalling pathways. These act on the transcription machinery but also on chromatin factors and ncRNA. The many ribosomal gene repeats are organised in a number of different chromatin states; active, poised, pseudosilent and repressed gene repeats. Some of these chromatin states are unique to the 47rRNA gene repeat and do not occur at other locations in the genome, such as the active state organised with the HMG protein UBF whereas other chromatin state are nucleosomal, harbouring both active and inactive histone marks. The number of repeats in a certain state varies on developmental stage and cell type; embryonic cells have more rRNA gene repeats organised in an open chromatin state, which is replaced by heterochromatin during differentiation, establishing different states depending on cell type. The 47S rRNA gene transcription is regulated in different ways depending on stimulus and chromatin state of individual gene repeats. This review will discuss the present knowledge about factors involved, such as chromatin remodelling factors NuRD, NoRC, CSB, B-WICH, histone modifying enzymes and histone chaperones, in altering gene expression and switching chromatin states in proliferation, differentiation, metabolic changes and stress responses.
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6
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Kara N, Krueger F, Rugg-Gunn P, Houseley J. Genome-wide analysis of DNA replication and DNA double-strand breaks using TrAEL-seq. PLoS Biol 2021; 19:e3000886. [PMID: 33760805 PMCID: PMC8021198 DOI: 10.1371/journal.pbio.3000886] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2020] [Revised: 04/05/2021] [Accepted: 02/17/2021] [Indexed: 02/07/2023] Open
Abstract
Faithful replication of the entire genome requires replication forks to copy large contiguous tracts of DNA, and sites of persistent replication fork stalling present a major threat to genome stability. Understanding the distribution of sites at which replication forks stall, and the ensuing fork processing events, requires genome-wide methods that profile replication fork position and the formation of recombinogenic DNA ends. Here, we describe Transferase-Activated End Ligation sequencing (TrAEL-seq), a method that captures single-stranded DNA 3' ends genome-wide and with base pair resolution. TrAEL-seq labels both DNA breaks and replication forks, providing genome-wide maps of replication fork progression and fork stalling sites in yeast and mammalian cells. Replication maps are similar to those obtained by Okazaki fragment sequencing; however, TrAEL-seq is performed on asynchronous populations of wild-type cells without incorporation of labels, cell sorting, or biochemical purification of replication intermediates, rendering TrAEL-seq far simpler and more widely applicable than existing replication fork direction profiling methods. The specificity of TrAEL-seq for DNA 3' ends also allows accurate detection of double-strand break sites after the initiation of DNA end resection, which we demonstrate by genome-wide mapping of meiotic double-strand break hotspots in a dmc1Δ mutant that is competent for end resection but not strand invasion. Overall, TrAEL-seq provides a flexible and robust methodology with high sensitivity and resolution for studying DNA replication and repair, which will be of significant use in determining mechanisms of genome instability.
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Affiliation(s)
- Neesha Kara
- Epigenetics Programme, Babraham Institute, Cambridge, United Kingdom
| | - Felix Krueger
- Babraham Bioinformatics, Babraham Institute, Cambridge, United Kingdom
| | - Peter Rugg-Gunn
- Epigenetics Programme, Babraham Institute, Cambridge, United Kingdom
| | - Jonathan Houseley
- Epigenetics Programme, Babraham Institute, Cambridge, United Kingdom
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7
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Schvartzman JB, Hernández P, Krimer DB. Replication Fork Barriers and Topological Barriers: Progression of DNA Replication Relies on DNA Topology Ahead of Forks. Bioessays 2020; 42:e1900204. [PMID: 32115727 DOI: 10.1002/bies.201900204] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2019] [Revised: 02/05/2020] [Indexed: 11/09/2022]
Abstract
During replication, the topology of DNA changes continuously in response to well-known activities of DNA helicases, polymerases, and topoisomerases. However, replisomes do not always progress at a constant speed and can slow-down and even stall at precise sites. The way these changes in the rate of replisome progression affect DNA topology is not yet well understood. The interplay of DNA topology and replication in several cases where progression of replication forks reacts differently to changes in DNA topology ahead is discussed here. It is proposed, there are at least two types of replication fork barriers: those that behave also as topological barriers and those that do not. Two-Dimensional (2D) agarose gel electrophoresis is the method of choice to distinguish between these two different types of replication fork barriers.
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Affiliation(s)
- Jorge B Schvartzman
- Department of Cellular and Molecular Biology, Centro de Investigaciones Biológicas Margarita Salas (CSIC), Ramiro de Maeztu 9, Madrid, 28040, Spain
| | - Pablo Hernández
- Department of Cellular and Molecular Biology, Centro de Investigaciones Biológicas Margarita Salas (CSIC), Ramiro de Maeztu 9, Madrid, 28040, Spain
| | - Dora B Krimer
- Department of Cellular and Molecular Biology, Centro de Investigaciones Biológicas Margarita Salas (CSIC), Ramiro de Maeztu 9, Madrid, 28040, Spain
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8
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Castán A, Hernández P, Krimer DB, Schvartzman JB. The abundance of Fob1 modulates the efficiency of rRFBs to stall replication forks. Nucleic Acids Res 2017; 45:10089-10102. [PMID: 28973451 PMCID: PMC5622318 DOI: 10.1093/nar/gkx655] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2017] [Accepted: 07/17/2017] [Indexed: 11/24/2022] Open
Abstract
In eukaryotes, ribosomal genes (rDNA) are organized in tandem repeats localized in one or a few clusters. Each repeat encompasses a transcription unit and a non-transcribed spacer. Replication forks moving in the direction opposite to transcription are blocked at specific sites called replication fork barriers (rRFBs) in the non-transcribed spacer close to the 3′ end of the transcription unit. Here, we investigated and quantified the efficiency of rRFBs in Saccharomyces cerevisiae and to this end transfected budding yeast cells that express dissimilar quantities of Fob1 with circular minichromosomes containing different copies of the minimal 20-bp DNA segment that bind Fob1. To identify fork stalling we used high-resolution 2D agarose gel electrophoresis. The results obtained indicated that neighbor DNA sequences and the relative abundance of Fob1 modulate the efficiency of rRFBs to stall replication forks.
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Affiliation(s)
- Alicia Castán
- Department of Cellular and Molecular Biology, Centro de Investigaciones Biológicas (CSIC), Ramiro de Maeztu 9, 28040 Madrid, Spain
| | - Pablo Hernández
- Department of Cellular and Molecular Biology, Centro de Investigaciones Biológicas (CSIC), Ramiro de Maeztu 9, 28040 Madrid, Spain
| | - Dora B Krimer
- Department of Cellular and Molecular Biology, Centro de Investigaciones Biológicas (CSIC), Ramiro de Maeztu 9, 28040 Madrid, Spain
| | - Jorge B Schvartzman
- Department of Cellular and Molecular Biology, Centro de Investigaciones Biológicas (CSIC), Ramiro de Maeztu 9, 28040 Madrid, Spain
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9
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Gadaleta MC, Noguchi E. Regulation of DNA Replication through Natural Impediments in the Eukaryotic Genome. Genes (Basel) 2017; 8:genes8030098. [PMID: 28272375 PMCID: PMC5368702 DOI: 10.3390/genes8030098] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2016] [Accepted: 03/03/2017] [Indexed: 02/07/2023] Open
Abstract
All living organisms need to duplicate their genetic information while protecting it from unwanted mutations, which can lead to genetic disorders and cancer development. Inaccuracies during DNA replication are the major cause of genomic instability, as replication forks are prone to stalling and collapse, resulting in DNA damage. The presence of exogenous DNA damaging agents as well as endogenous difficult-to-replicate DNA regions containing DNA–protein complexes, repetitive DNA, secondary DNA structures, or transcribing RNA polymerases, increases the risk of genomic instability and thus threatens cell survival. Therefore, understanding the cellular mechanisms required to preserve the genetic information during S phase is of paramount importance. In this review, we will discuss our current understanding of how cells cope with these natural impediments in order to prevent DNA damage and genomic instability during DNA replication.
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Affiliation(s)
- Mariana C Gadaleta
- Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, PA 19102, USA.
| | - Eishi Noguchi
- Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, PA 19102, USA.
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10
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Abstract
Genomic instability is a hallmark of cancer and a common feature of human disorders, characterized by growth defects, neurodegeneration, cancer predisposition, and aging. Recent evidence has shown that DNA replication stress is a major driver of genomic instability and tumorigenesis. Cells can undergo mitosis with under-replicated DNA or unresolved DNA structures, and specific pathways are dedicated to resolving these structures during mitosis, suggesting that mitotic rescue from replication stress (MRRS) is a key process influencing genome stability and cellular homeostasis. Deregulation of MRRS following oncogene activation or loss-of-function of caretaker genes may be the cause of chromosomal aberrations that promote cancer initiation and progression. In this review, we discuss the causes and consequences of replication stress, focusing on its persistence in mitosis as well as the mechanisms and factors involved in its resolution, and the potential impact of incomplete replication or aberrant MRRS on tumorigenesis, aging and disease.
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Affiliation(s)
- Michalis Fragkos
- a CNRS UMR8200 , University Paris-Saclay , Gustave Roussy, Villejuif , France
| | - Valeria Naim
- a CNRS UMR8200 , University Paris-Saclay , Gustave Roussy, Villejuif , France
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11
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Abstract
DNA topological transitions occur when replication forks encounter other DNA transactions such as transcription. Failure in resolving such conflicts leads to generation of aberrant replication and transcription intermediates that might have adverse effects on genome stability. Cells have evolved numerous surveillance mechanisms to avoid, tolerate, and resolve such replication-transcription conflicts. Defects or non-coordination in such cellular mechanisms might have catastrophic effect on cell viability. In this chapter, we review consequences of replication encounters with transcription and its associated events, topological challenges, and how these inevitable conflicts alter the genome structure and functions.
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12
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Agrawal S, Ganley ARD. Complete Sequence Construction of the Highly Repetitive Ribosomal RNA Gene Repeats in Eukaryotes Using Whole Genome Sequence Data. Methods Mol Biol 2016; 1455:161-181. [PMID: 27576718 DOI: 10.1007/978-1-4939-3792-9_13] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The ribosomal RNA genes (rDNA) encode the major rRNA species of the ribosome, and thus are essential across life. These genes are highly repetitive in most eukaryotes, forming blocks of tandem repeats that form the core of nucleoli. The primary role of the rDNA in encoding rRNA has been long understood, but more recently the rDNA has been implicated in a number of other important biological phenomena, including genome stability, cell cycle, and epigenetic silencing. Noncoding elements, primarily located in the intergenic spacer region, appear to mediate many of these phenomena. Although sequence information is available for the genomes of many organisms, in almost all cases rDNA repeat sequences are lacking, primarily due to problems in assembling these intriguing regions during whole genome assemblies. Here, we present a method to obtain complete rDNA repeat unit sequences from whole genome assemblies. Limitations of next generation sequencing (NGS) data make them unsuitable for assembling complete rDNA unit sequences; therefore, the method we present relies on the use of Sanger whole genome sequence data. Our method makes use of the Arachne assembler, which can assemble highly repetitive regions such as the rDNA in a memory-efficient way. We provide a detailed step-by-step protocol for generating rDNA sequences from whole genome Sanger sequence data using Arachne, for refining complete rDNA unit sequences, and for validating the sequences obtained. In principle, our method will work for any species where the rDNA is organized into tandem repeats. This will help researchers working on species without a complete rDNA sequence, those working on evolutionary aspects of the rDNA, and those interested in conducting phylogenetic footprinting studies with the rDNA.
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Affiliation(s)
- Saumya Agrawal
- Institute of Natural and Mathematical Sciences, Massey University, Private Bag 102-904, Auckland, 0632, New Zealand.
- School of Biological Sciences, University of Auckland, Auckland, New Zealand.
| | - Austen R D Ganley
- Institute of Natural and Mathematical Sciences, Massey University, Private Bag 102-904, Auckland, 0632, New Zealand.
- School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland, 1142, New Zealand.
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13
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The Human RNA Polymerase I Transcription Terminator Complex Acts as a Replication Fork Barrier That Coordinates the Progress of Replication with rRNA Transcription Activity. Mol Cell Biol 2015; 35:1871-81. [PMID: 25776556 DOI: 10.1128/mcb.01521-14] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2014] [Accepted: 03/09/2015] [Indexed: 01/28/2023] Open
Abstract
In S phase, the replication and transcription of genomic DNA need to accommodate each other, otherwise their machineries collide, with chromosomal instability as a possible consequence. Here, we characterized the human replication fork barrier (RFB) that is present downstream from the 47S pre-rRNA gene (ribosomal DNA [rDNA]). We found that the most proximal transcription terminator, Sal box T1, acts as a polar RFB, while the other, Sal box T4/T5, arrests replication forks bidirectionally. The fork-arresting activity at these sites depends on polymerase I (Pol I) transcription termination factor 1 (TTF-1) and a replisome component, TIMELESS (TIM). We also found that the RFB activity was linked to rDNA copies with hypomethylated CpG and coincided with the time that actively transcribed rRNA genes are replicated. Failed fork arrest at RFB sites led to a slowdown of fork progression moving in the opposite direction to rRNA transcription. Chemical inhibition of transcription counteracted this deceleration of forks, indicating that rRNA transcription impedes replication in the absence of RFB activity. Thus, our results reveal a role of RFB for coordinating the progression of replication and transcription activity in highly transcribed rRNA genes.
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14
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Muchová V, Amiard S, Mozgová I, Dvořáčková M, Gallego ME, White C, Fajkus J. Homology-dependent repair is involved in 45S rDNA loss in plant CAF-1 mutants. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2015; 81:198-209. [PMID: 25359579 PMCID: PMC4309414 DOI: 10.1111/tpj.12718] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2014] [Revised: 10/23/2014] [Accepted: 10/24/2014] [Indexed: 05/19/2023]
Abstract
Arabidopsis thaliana mutants in FAS1 and FAS2 subunits of chromatin assembly factor 1 (CAF1) show progressive loss of 45S rDNA copies and telomeres. We hypothesized that homology-dependent DNA damage repair (HDR) may contribute to the loss of these repeats in fas mutants. To test this, we generated double mutants by crossing fas mutants with knock-out mutants in RAD51B, one of the Rad51 paralogs of A. thaliana. Our results show that the absence of RAD51B decreases the rate of rDNA loss, confirming the implication of RAD51B-dependent recombination in rDNA loss in the CAF1 mutants. Interestingly, this effect is not observed for telomeric repeat loss, which thus differs from that acting in rDNA loss. Involvement of DNA damage repair in rDNA dynamics in fas mutants is further supported by accumulation of double-stranded breaks (measured as γ-H2AX foci) in 45S rDNA. Occurrence of the foci is not specific for S-phase, and is ATM-independent. While the foci in fas mutants occur both in the transcribed (intranucleolar) and non-transcribed (nucleoplasmic) fraction of rDNA, double fas rad51b mutants show a specific increase in the number of the intranucleolar foci. These results suggest that the repair of double-stranded breaks present in the transcribed rDNA region is RAD51B dependent and that this contributes to rDNA repeat loss in fas mutants, presumably via the single-stranded annealing recombination pathway. Our results also highlight the importance of proper chromatin assembly in the maintenance of genome stability.
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Affiliation(s)
- Veronika Muchová
- Mendel Centre for Plant Genomics and Proteomics, CEITEC, Masaryk University, Kamenice 5, CZ-62500, Brno, Czech Republic; Laboratory of Functional Genomics and Proteomics, National Centre for Biomolecular Research, Faculty of Science, Masaryk University, Kotlářská 2, CZ-61137, Brno, Czech Republic
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15
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Transcription-replication encounters, consequences and genomic instability. Nat Struct Mol Biol 2013; 20:412-8. [PMID: 23552296 DOI: 10.1038/nsmb.2543] [Citation(s) in RCA: 204] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2012] [Accepted: 02/07/2013] [Indexed: 12/16/2022]
Abstract
To ensure accurate duplication of genetic material, the replication fork must overcome numerous natural obstacles on its way, including transcription complexes engaged along the same template. Here we review the various levels of interdependence between transcription and replication processes and how different types of encounters between RNA- and DNA-polymerase complexes may result in clashes of those machineries on the DNA template and thus increase genomic instability. In addition, we summarize strategies evolved in bacteria and eukaryotes to minimize the consequences of collisions, including R-loop formation and topological stresses.
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16
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A telomerase-independent component of telomere loss in chromatin assembly factor 1 mutants of Arabidopsis thaliana. Chromosoma 2013; 122:285-93. [PMID: 23564254 DOI: 10.1007/s00412-013-0400-6] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2013] [Revised: 02/14/2013] [Accepted: 02/19/2013] [Indexed: 01/23/2023]
Abstract
Dysfunction of chromatin assembly factor 1 in FASCIATA mutants (fas) of Arabidopsis thaliana results in progressive loss of telomeric DNA. Although replicative telomere shortening is typically associated with incomplete resynthesis of their ends by telomerase, no change in telomerase activity could be detected in vitro in extracts from fas mutants. Besides a possible telomerase malfunction, the telomere shortening in fas mutants could presumably be due to problems with conventional replication of telomeres. To distinguish between the possible contribution of suboptimal function of telomerase in fas mutants under in vivo conditions and problems in conventional telomere replication, we crossed fas and tert (telomerase reverse transcriptase) knockout mutants and analyzed telomere shortening in segregated fas mutants, tert mutants, and double fas tert mutants in parallel. We demonstrate that fas tert knockouts show greater replicative telomere shortening than that observed even in the complete absence of telomerase (tert mutants). While the effect of tert and fas mutations on telomere lengths in double mutants is additive, manifestations of telomere dysfunction in double fas tert mutants (frequency of anaphase bridges, onset of chromosome end fusions, and common involvement of 45S rDNA in chromosome fusion sites) are similar to those in tert mutants. We conclude that in addition to possible impairment of telomerase action, a further mechanism contributes to telomere shortening in fas mutants.
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17
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Abstract
The eukaryotic cell replicates its chromosomal DNA with almost absolute fidelity in the course of every cell cycle. This accomplishment is remarkable considering that the conditions for DNA replication are rarely ideal. The replication machinery encounters a variety of obstacles on the chromosome, including damaged template DNA. In addition, a number of chromosome regions are considered to be difficult to replicate owing to DNA secondary structures and DNA binding proteins required for various transactions on the chromosome. Under these conditions, replication forks stall or break, posing grave threats to genomic integrity. How does the cell combat such stressful conditions during DNA replication? The replication fork protection complex (FPC) may help answer this question. Recent studies have demonstrated that the FPC is required for the smooth passage of replication forks at difficult-to-replicate genomic regions and plays a critical role in coordinating multiple genome maintenance processes at the replication fork.
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Affiliation(s)
- Adam R. Leman
- Department of Biochemistry and Molecular Biology; Drexel University College of Medicine; Philadelphia, PA USA
| | - Eishi Noguchi
- Department of Biochemistry and Molecular Biology; Drexel University College of Medicine; Philadelphia, PA USA
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18
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Schvartzman JB, Martínez-Robles ML, López V, Hernández P, Krimer DB. 2D gels and their third-dimension potential. Methods 2012; 57:170-8. [PMID: 22465282 DOI: 10.1016/j.ymeth.2012.03.013] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2011] [Revised: 03/03/2012] [Accepted: 03/10/2012] [Indexed: 11/19/2022] Open
Abstract
Two-dimensional (2D) agarose gel electrophoresis is one of the most powerful methods to analyze the mass and shape of replication intermediates. It is often use to map replication origins but it is also useful to characterize termination of replication, replication fork barriers and even replication fork reversal. Here, we present protocols, figures and movies with a thorough description of different modes of replication for linear DNA fragments and the corresponding patterns they generate in 2D gels.
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MESH Headings
- Autoradiography
- DNA Replication
- DNA, Bacterial/chemistry
- DNA, Bacterial/genetics
- DNA, Bacterial/isolation & purification
- DNA, Circular/chemistry
- DNA, Circular/genetics
- DNA, Circular/isolation & purification
- Electrophoresis, Agar Gel/methods
- Electrophoresis, Gel, Two-Dimensional/methods
- Microscopy, Atomic Force
- Models, Molecular
- Nucleic Acid Conformation
- Plasmids/chemistry
- Plasmids/genetics
- Plasmids/isolation & purification
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Affiliation(s)
- Jorge B Schvartzman
- Department of Cell Proliferation and Development, Centro de Investigaciones Biológicas (CSIC), Madrid, Spain.
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19
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Houseley J, Tollervey D. Repeat expansion in the budding yeast ribosomal DNA can occur independently of the canonical homologous recombination machinery. Nucleic Acids Res 2011; 39:8778-91. [PMID: 21768125 PMCID: PMC3203602 DOI: 10.1093/nar/gkr589] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Major eukaryotic genomic elements, including the ribosomal DNA (rDNA), are composed of repeated sequences with well-defined copy numbers that must be maintained by regulated recombination. Although mechanisms that instigate rDNA recombination have been identified, none are directional and they therefore cannot explain precise repeat number control. Here, we show that yeast lacking histone chaperone Asf1 undergo reproducible rDNA repeat expansions. These expansions do not require the replication fork blocking protein Fob1 and are therefore independent of known rDNA expansion mechanisms. We propose the existence of a regulated rDNA repeat gain pathway that becomes constitutively active in asf1Δ mutants. Cells lacking ASF1 accumulate rDNA repeats with high fidelity in a processive manner across multiple cell divisions. The mechanism of repeat gain is dependent on highly repetitive sequence but, surprisingly, is independent of the homologous recombination proteins Rad52, Rad51 and Rad59. The expansion mechanism is compromised by mutations that decrease the processivity of DNA replication, which leads to progressive loss of rDNA repeats. Our data suggest that a novel mode of break-induced replication occurs in repetitive DNA that is dependent on high homology but does not require the canonical homologous recombination machinery.
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Affiliation(s)
- Jonathan Houseley
- Wellcome Trust Centre for Cell Biology, University of Edinburgh, Edinburgh, EH9 3JR, UK.
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20
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Rodríguez-Sánchez L, Rodríguez-López M, García Z, Tenorio-Gómez M, Schvartzman JB, Krimer DB, Hernández P. The fission yeast rDNA-binding protein Reb1 regulates G1 phase under nutritional stress. J Cell Sci 2010; 124:25-34. [PMID: 21118960 DOI: 10.1242/jcs.070987] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Yeast Reb1 and its mammalian ortholog TTF1 are conserved Myb-type DNA-binding proteins that bind to specific sites near the 3'-end of rRNA genes (rDNA). Here, they participate in the termination of transcription driven by RNA polymerase I and block DNA replication forks approaching in the opposite direction. We found that Schizosaccharomyces pombe Reb1 also upregulates transcription of the ste9(+) gene that is required for nitrogen-starvation-induced growth arrest with a G1 DNA content and sexual differentiation. Ste9 activates the anaphase-promoting complex or cyclosome ('APC/C') in G1, targeting B-cyclin for proteasomal degradation in response to nutritional stress. Reb1 binds in vivo and in vitro to a specific DNA sequence at the promoter of ste9(+), similar to the sequence recognized in the rDNA, and this binding is required for ste9(+) transcriptional activation and G1 arrest. This suggests that Reb1 acts as a link between rDNA metabolism and cell cycle control in response to nutritional stress. In agreement with this new role for Reb1 in the regulation of the G1-S transition, reb1Δ and wee1(ts) mutations are synthetically lethal owing to the inability of these cells to lengthen G1 before entering S phase. Similarly, reb1Δ cdc10(ts) cells are unable to arrest in G1 and die at the semi-permissive temperature.
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Affiliation(s)
- Leonor Rodríguez-Sánchez
- Department of Cell Proliferation and Development, Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Ramiro de Maeztu 9, 28040 Madrid, Spain
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21
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High-resolution mapping of points of site-specific replication stalling. Methods Mol Biol 2009. [PMID: 19563109 DOI: 10.1007/978-1-60327-815-7_12] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
Abstract
Genetic instability due to stalled replication forks is thought to underlie a number of human diseases, such as premature ageing and cancer susceptibility syndromes. In addition, site-specific stalling occurs at some genetic loci. A detailed understanding of the topology of the stalled replication fork gives a valuable insight into the causes and mechanisms of replication stalling. The method described here allows mapping of the position of the 3'-end of the nascent leading or lagging strand at the replication fork, stalled at a site-specific barrier. The replicating DNA is purified, digested with restriction enzymes, and enriched by BND-cellulose chromatography. The DNA is separated on a sequencing gel, transferred to a membrane, and hybridised to a strand-specific probe. The data obtained using this method allow determining the position of the 3'-end of the nascent strand at a stalled fork with a one-nucleotide resolution.
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22
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Dalgaard JZ, Eydmann T, Koulintchenko M, Sayrac S, Vengrova S, Yamada-Inagawa T. Random and site-specific replication termination. Methods Mol Biol 2009; 521:35-53. [PMID: 19563100 DOI: 10.1007/978-1-60327-815-7_3] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Bi-directionality is a common feature observed for genomic replication for all three phylogenetic kingdoms: Eubacteria, Archaea, and Eukaryotes. A consequence of bi-directional replication, where the two replication forks initiated at an origin move away from each other, is that the replication termination will occur at positions away from the origin sequence(s). The replication termination processes are therefore physically and mechanistically dissociated from the replication initiation. The replication machinery is a highly processive complex that in short time copies huge numbers of bases while competing for the DNA substrate with histones, transcription factors, and other DNA-binding proteins. Importantly, the replication machinery generally wins out; meanwhile, when converging forks meet termination occurs, thus preventing over-replication and genetic instability. Very different scenarios for the replication termination processes have been described for the three phylogenetic kingdoms. In eubacterial genomes replication termination is site specific, while in archaea and eukaryotes termination is thought to occur randomly within zones where converging replication forks meet. However, a few site-specific replication barrier elements that mediate replication termination have been described in eukaryotes. This review gives an overview about what is known about replication termination, with a focus on these natural site-specific replication termination sites.
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23
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Eydmann T, Sommariva E, Inagawa T, Mian S, Klar AJS, Dalgaard JZ. Rtf1-mediated eukaryotic site-specific replication termination. Genetics 2008; 180:27-39. [PMID: 18723894 PMCID: PMC2535681 DOI: 10.1534/genetics.108.089243] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2008] [Accepted: 06/30/2008] [Indexed: 11/18/2022] Open
Abstract
The molecular mechanisms mediating eukaryotic replication termination and pausing remain largely unknown. Here we present the molecular characterization of Rtf1 that mediates site-specific replication termination at the polar Schizosaccharomyces pombe barrier RTS1. We show that Rtf1 possesses two chimeric myb/SANT domains: one is able to interact with the repeated motifs encoded by the RTS1 element as well as the elements enhancer region, while the other shows only a weak DNA binding activity. In addition we show that the C-terminal tail of Rtf1 mediates self-interaction, and deletion of this tail has a dominant phenotype. Finally, we identify a point mutation in Rtf1 domain I that converts the RTS1 element into a replication barrier of the opposite polarity. Together our data establish that multiple protein DNA and protein-protein interactions between Rtf1 molecules and both the repeated motifs and the enhancer region of RTS1 are required for site-specific termination at the RTS1 element.
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Affiliation(s)
- T Eydmann
- Marie Curie Research Institute, The Chart, Oxted RH8 0TL, United Kingdom
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24
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Mayán-Santos MD, Martínez-Robles ML, Hernández P, Schvartzman JB, Krimer DB. A redundancy of processes that cause replication fork stalling enhances recombination at two distinct sites in yeast rDNA. Mol Microbiol 2008; 69:361-75. [PMID: 18485068 DOI: 10.1111/j.1365-2958.2008.06278.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
DNA recombination was investigated by monitoring integration at the rDNA of a circular minichromosome containing a 35S minigene and a replication fork barrier (RFB). The effects of replication fork stalling on integration were studied in wild-type, FOB1Delta, SIR2Delta and the double mutant FOB1DeltaSIR2Delta cells. The results obtained confirmed that Sir2p represses and replication fork stalling enhances integration of the minichromosome. This integration, however, only took place at two distinct sites: the RFB and the 3' end of the 35S gene. For integration to take place at the 35S gene, replication fork stalling must occur at the 3' end of the gene in both the minichromosome and the chromosomal repeats. Integration at the RFB, on the other hand, occurred readily in FOB1Delta cells, indicating that more than a single mechanism triggers homologous recombination at this site. Altogether, these observations strongly suggest that the main role for replication fork stalling at the rDNA locus is to promote homologous recombination rather than just to prevent head-on collision of transcription and replication as originally thought.
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Affiliation(s)
- M D Mayán-Santos
- Departamento de Biología Celular y del Desarrollo, Centro de Investigaciones Biológicas (CSIC), Ramiro de Maeztu 9, 28040 Madrid, Spain
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25
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Hyvärinen AK, Pohjoismäki JLO, Reyes A, Wanrooij S, Yasukawa T, Karhunen PJ, Spelbrink JN, Holt IJ, Jacobs HT. The mitochondrial transcription termination factor mTERF modulates replication pausing in human mitochondrial DNA. Nucleic Acids Res 2007; 35:6458-74. [PMID: 17884915 PMCID: PMC2095818 DOI: 10.1093/nar/gkm676] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The mammalian mitochondrial transcription termination factor mTERF binds with high affinity to a site within the tRNA(Leu(UUR)) gene and regulates the amount of read through transcription from the ribosomal DNA into the remaining genes of the major coding strand of mitochondrial DNA (mtDNA). Electrophoretic mobility shift assays (EMSA) and SELEX, using mitochondrial protein extracts from cells induced to overexpress mTERF, revealed novel, weaker mTERF-binding sites, clustered in several regions of mtDNA, notably in the major non-coding region (NCR). Such binding in vivo was supported by mtDNA immunoprecipitation. Two-dimensional neutral agarose gel electrophoresis (2DNAGE) and 5' end mapping by ligation-mediated PCR (LM-PCR) identified the region of the canonical mTERF-binding site as a replication pause site. The strength of pausing was modulated by the expression level of mTERF. mTERF overexpression also affected replication pausing in other regions of the genome in which mTERF binding was found. These results indicate a role for TERF in mtDNA replication, in addition to its role in transcription. We suggest that mTERF could provide a system for coordinating the passage of replication and transcription complexes, analogous with replication pause-region binding proteins in other systems, whose main role is to safeguard the integrity of the genome whilst facilitating its efficient expression.
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Affiliation(s)
- Anne K. Hyvärinen
- Institute of Medical Technology and Tampere University Hospital, FI-33014, University of Tampere, Finland, MRC-Dunn Human Nutrition Unit, Cambridge, UK, Department of Forensic Medicine and Tampere University Hospital, FI-33014, University of Tampere, Finland and Institute of Biomedical and Life Sciences, University of Glasgow, Scotland, UK
| | - Jaakko L. O. Pohjoismäki
- Institute of Medical Technology and Tampere University Hospital, FI-33014, University of Tampere, Finland, MRC-Dunn Human Nutrition Unit, Cambridge, UK, Department of Forensic Medicine and Tampere University Hospital, FI-33014, University of Tampere, Finland and Institute of Biomedical and Life Sciences, University of Glasgow, Scotland, UK
| | - Aurelio Reyes
- Institute of Medical Technology and Tampere University Hospital, FI-33014, University of Tampere, Finland, MRC-Dunn Human Nutrition Unit, Cambridge, UK, Department of Forensic Medicine and Tampere University Hospital, FI-33014, University of Tampere, Finland and Institute of Biomedical and Life Sciences, University of Glasgow, Scotland, UK
| | - Sjoerd Wanrooij
- Institute of Medical Technology and Tampere University Hospital, FI-33014, University of Tampere, Finland, MRC-Dunn Human Nutrition Unit, Cambridge, UK, Department of Forensic Medicine and Tampere University Hospital, FI-33014, University of Tampere, Finland and Institute of Biomedical and Life Sciences, University of Glasgow, Scotland, UK
| | - Takehiro Yasukawa
- Institute of Medical Technology and Tampere University Hospital, FI-33014, University of Tampere, Finland, MRC-Dunn Human Nutrition Unit, Cambridge, UK, Department of Forensic Medicine and Tampere University Hospital, FI-33014, University of Tampere, Finland and Institute of Biomedical and Life Sciences, University of Glasgow, Scotland, UK
| | - Pekka J. Karhunen
- Institute of Medical Technology and Tampere University Hospital, FI-33014, University of Tampere, Finland, MRC-Dunn Human Nutrition Unit, Cambridge, UK, Department of Forensic Medicine and Tampere University Hospital, FI-33014, University of Tampere, Finland and Institute of Biomedical and Life Sciences, University of Glasgow, Scotland, UK
| | - Johannes N. Spelbrink
- Institute of Medical Technology and Tampere University Hospital, FI-33014, University of Tampere, Finland, MRC-Dunn Human Nutrition Unit, Cambridge, UK, Department of Forensic Medicine and Tampere University Hospital, FI-33014, University of Tampere, Finland and Institute of Biomedical and Life Sciences, University of Glasgow, Scotland, UK
| | - Ian J. Holt
- Institute of Medical Technology and Tampere University Hospital, FI-33014, University of Tampere, Finland, MRC-Dunn Human Nutrition Unit, Cambridge, UK, Department of Forensic Medicine and Tampere University Hospital, FI-33014, University of Tampere, Finland and Institute of Biomedical and Life Sciences, University of Glasgow, Scotland, UK
| | - Howard T. Jacobs
- Institute of Medical Technology and Tampere University Hospital, FI-33014, University of Tampere, Finland, MRC-Dunn Human Nutrition Unit, Cambridge, UK, Department of Forensic Medicine and Tampere University Hospital, FI-33014, University of Tampere, Finland and Institute of Biomedical and Life Sciences, University of Glasgow, Scotland, UK
- *To whom correspondence should be addressed. +358 3 3551 7731+358 3 3551 7710; E-mail:
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26
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Abstract
Accurate and complete replication of the genome in every cell division is a prerequisite of genomic stability. Thus, both prokaryotic and eukaryotic replication forks are extremely precise and robust molecular machines that have evolved to be up to the task. However, it has recently become clear that the replication fork is more of a hurdler than a runner: it must overcome various obstacles present on its way. Such obstacles can be called natural impediments to DNA replication, as opposed to external and genetic factors. Natural impediments to DNA replication are particular DNA binding proteins, unusual secondary structures in DNA, and transcription complexes that occasionally (in eukaryotes) or constantly (in prokaryotes) operate on replicating templates. This review describes the mechanisms and consequences of replication stalling at various natural impediments, with an emphasis on the role of replication stalling in genomic instability.
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Affiliation(s)
- Ekaterina V. Mirkin
- Department of Biochemistry and Molecular Genetics, College of Medicine, University of Illinois at Chicago, Chicago, Illinois 60607
| | - Sergei M. Mirkin
- Department of Biochemistry and Molecular Genetics, College of Medicine, University of Illinois at Chicago, Chicago, Illinois 60607
- Corresponding author. Present address: Department of Biology, Tufts University, Medford, MA 02155. Phone: (617) 627-4794. Fax: (617) 627-3805. E-mail:
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27
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Kwong LN, Shedlovsky A, Biehl BS, Clipson L, Pasch CA, Dove WF. Identification of Mom7, a novel modifier of Apc(Min/+) on mouse chromosome 18. Genetics 2007; 176:1237-44. [PMID: 17435219 PMCID: PMC1894587 DOI: 10.1534/genetics.107.071217] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
The Apc(Min) mouse model of colorectal cancer provides a discrete, quantitative measurement of tumor multiplicity, allowing for robust quantitative trait locus analysis. This advantage has previously been used to uncover polymorphic modifiers of the Min phenotype: Mom1, which is partly explained by Pla2g2a; Mom2, a spontaneous mutant modifier; and Mom3, which was discovered in an outbred cross. Here, we describe the localization of a novel modifier, Mom7, to the pericentromeric region of chromosome 18. Mom7 was mapped in crosses involving four inbred strains: C57BL/6J (B6), BTBR/Pas (BTBR), AKR/J (AKR), and A/J. There are at least two distinct alleles of Mom7: the recessive, enhancing BTBR, AKR, and A/J alleles and the dominant, suppressive B6 allele. Homozygosity for the enhancing alleles increases tumor number by approximately threefold in the small intestine on both inbred and F(1) backgrounds. Congenic line analysis has narrowed the Mom7 region to within 7.4 Mb of the centromere, 28 Mb proximal to Apc. Analysis of SNP data from various genotyping projects suggests that the region could be as small as 4.4 Mb and that there may be five or more alleles of Mom7 segregating among the many strains of inbred mice. This has implications for experiments involving Apc(Min) and comparisons between different or mixed genetic backgrounds.
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Affiliation(s)
- Lawrence N. Kwong
- McArdle Laboratory for Cancer Research and Laboratory of Genetics, University of Wisconsin, Madison, Wisconsin 53706
| | - Alexandra Shedlovsky
- McArdle Laboratory for Cancer Research and Laboratory of Genetics, University of Wisconsin, Madison, Wisconsin 53706
| | - Bryan S. Biehl
- McArdle Laboratory for Cancer Research and Laboratory of Genetics, University of Wisconsin, Madison, Wisconsin 53706
| | - Linda Clipson
- McArdle Laboratory for Cancer Research and Laboratory of Genetics, University of Wisconsin, Madison, Wisconsin 53706
| | - Cheri A. Pasch
- McArdle Laboratory for Cancer Research and Laboratory of Genetics, University of Wisconsin, Madison, Wisconsin 53706
| | - William F. Dove
- McArdle Laboratory for Cancer Research and Laboratory of Genetics, University of Wisconsin, Madison, Wisconsin 53706
- Corresponding author: McArdle Laboratory for Cancer Research, 1400 University Ave., Madison, WI 53706. E-mail:
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28
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Gray SJ, Liu G, Altman AL, Small LE, Fanning E. Discrete functional elements required for initiation activity of the Chinese hamster dihydrofolate reductase origin beta at ectopic chromosomal sites. Exp Cell Res 2006; 313:109-20. [PMID: 17078947 PMCID: PMC1810229 DOI: 10.1016/j.yexcr.2006.09.020] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2006] [Revised: 09/20/2006] [Accepted: 09/21/2006] [Indexed: 01/06/2023]
Abstract
The Chinese hamster dihydrofolate reductase (DHFR) DNA replication initiation region, the 5.8 kb ori-beta, can function as a DNA replicator at random ectopic chromosomal sites in hamster cells. We report a detailed genetic analysis of the DiNucleotide Repeat (DNR) element, one of several sequence elements necessary for ectopic ori-beta activity. Deletions within ori-beta identified a 132 bp core region within the DNR element, consisting mainly of dinucleotide repeats, and a downstream region that are required for ori-beta initiation activity at non-specific ectopic sites in hamster cells. Replacement of the DNR element with Xenopus or mouse transcriptional elements from rDNA genes restored full levels of initiation activity, but replacement with a nucleosome positioning element or a viral intron sequence did not. The requirement for the DNR element and three other ori-beta sequence elements was conserved when ori-beta activity was tested at either random sites or at a single specific ectopic chromosomal site in human cells. These results confirm the importance of specific cis-acting elements in directing the initiation of DNA replication in mammalian cells, and provide new evidence that transcriptional elements can functionally substitute for one of these elements in ori-beta.
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Affiliation(s)
- Steven J. Gray
- Department of Biological Sciences and the Vanderbilt-Ingram Cancer Center, Vanderbilt University, Nashville, Tennessee 37235
| | - Guoqi Liu
- Department of Biological Sciences and the Vanderbilt-Ingram Cancer Center, Vanderbilt University, Nashville, Tennessee 37235
| | - Amy L. Altman
- Department of Biological Sciences and the Vanderbilt-Ingram Cancer Center, Vanderbilt University, Nashville, Tennessee 37235
| | - Lawrence E. Small
- Department of Biological Sciences and the Vanderbilt-Ingram Cancer Center, Vanderbilt University, Nashville, Tennessee 37235
| | - Ellen Fanning
- Department of Biological Sciences and the Vanderbilt-Ingram Cancer Center, Vanderbilt University, Nashville, Tennessee 37235
- * To whom correspondence should be addressed: Department of Biological Sciences, Vanderbilt University, VU Station B 351634 Nashville, TN 37235-1634 Tel: (615) 343-5677 Fax: (615) 343-6707
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29
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Krings G, Bastia D. Molecular architecture of a eukaryotic DNA replication terminus-terminator protein complex. Mol Cell Biol 2006; 26:8061-74. [PMID: 16940176 PMCID: PMC1636744 DOI: 10.1128/mcb.01102-06] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
DNA replication forks pause at programmed fork barriers within nontranscribed regions of the ribosomal DNA (rDNA) genes of many eukaryotes to coordinate and regulate replication, transcription, and recombination. The mechanism of eukaryotic fork arrest remains unknown. In Schizosaccharomyces pombe, the promiscuous DNA binding protein Sap1 not only causes polar fork arrest at the rDNA fork barrier Ter1 but also regulates mat1 imprinting at SAS1 without fork pausing. Towards an understanding of eukaryotic fork arrest, we probed the interactions of Sap1 with Ter1 as contrasted with SAS1. The Sap1 dimer bound Ter1 with high affinity at one face of the DNA, contacting successive major grooves. The complex displayed translational symmetry. In contrast, Sap1 subunits approached SAS1 from opposite helical faces, forming a low-affinity complex with mirror image rotational symmetry. The alternate symmetries were reflected in distinct Sap1-induced helical distortions. Importantly, modulating protein-DNA interactions of the fork-proximal Sap1 subunit with the nonnatural binding site DR2 affected blocking efficiency without changes in binding affinity or binding mode but with alterations in Sap1-induced DNA distortion. The results reveal that Sap1-DNA affinity alone is insufficient to account for fork arrest and suggest that Sap1 binding-induced structural changes may result in formation of a competent fork-blocking complex.
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Affiliation(s)
- Gregor Krings
- Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC 29425, USA
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30
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Coulon S, Noguchi E, Noguchi C, Du LL, Nakamura TM, Russell P. Rad22Rad52-dependent repair of ribosomal DNA repeats cleaved by Slx1-Slx4 endonuclease. Mol Biol Cell 2006; 17:2081-90. [PMID: 16467377 PMCID: PMC1415312 DOI: 10.1091/mbc.e05-11-1006] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Slx1 and Slx4 are subunits of a structure-specific DNA endonuclease that is found in Saccharomyces cerevisiae, Schizosaccharomyces pombe, and other eukaryotic species. It is thought to initiate recombination events or process recombination structures that occur during the replication of the tandem repeats of the ribosomal DNA (rDNA) locus. Here, we present evidence that fission yeast Slx1-Slx4 initiates homologous recombination events in the rDNA repeats that are processed by a mechanism that requires Rad22 (Rad52 homologue) but not Rhp51 (Rad51 homologue). Slx1 is required to generate approximately 50% of the spontaneous Rad22 DNA repair foci that occur in cycling cells. Most of these foci colocalize with the nucleolus, which contains the rDNA repeats. The increased fork pausing at the replication fork barriers in the rDNA repeats in a strain that lacks Rqh1 DNA helicase is further increased by expression of a dominant negative form of Slx1. These data suggest that Slx1-Slx4 cleaves paused replication forks in the rDNA, leading to Rad22-dependent homologous recombination that is used to maintain rDNA copy number.
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Affiliation(s)
- Stéphane Coulon
- Department of Molecular Biology, The Scripps Research Institute, La Jolla, CA 92037, USA
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31
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Mejía-Ramírez E, Sánchez-Gorostiaga A, Krimer DB, Schvartzman JB, Hernández P. The mating type switch-activating protein Sap1 Is required for replication fork arrest at the rRNA genes of fission yeast. Mol Cell Biol 2005; 25:8755-61. [PMID: 16166653 PMCID: PMC1265749 DOI: 10.1128/mcb.25.19.8755-8761.2005] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Schizosaccharomyces pombe rRNA genes contain three replication fork barriers (RFB1-3) located in the nontranscribed spacer. RFB2 and RFB3 require binding of the transcription terminator factor Reb1p to two identical recognition sequences that colocalize with these barriers. RFB1, which is the strongest of the three barriers, functions in a Reb1p-independent manner, and cognate DNA-binding proteins for this barrier have not been identified yet. Here we functionally define RFB1 within a 78-bp sequence located near the 3' end of the rRNA coding region. A protein that specifically binds to this sequence was purified by affinity chromatography and identified as Sap1p by mass spectrometry. Specific binding to RFB1 was confirmed by using Sap1p expressed in Escherichia coli. Sap1p is essential for viability and is required for efficient mating-type switching. Mutations in RFB1 that precluded formation of the Sap1p-RFB1 complex systematically abolished replication barrier function, indicating that Sap1p is required for replication fork blockage at RFB1.
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Affiliation(s)
- Eva Mejía-Ramírez
- Departamento de Biología Celular y del Desarrollo, Centro de Investigaciones Biológicas (CSIC), Ramiro de Maeztu 9, 28040 Madrid, Spain
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32
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Krings G, Bastia D. Sap1p binds to Ter1 at the ribosomal DNA of Schizosaccharomyces pombe and causes polar replication fork arrest. J Biol Chem 2005; 280:39135-42. [PMID: 16195226 DOI: 10.1074/jbc.m508996200] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Eukaryotic DNA replication forks stall at natural replication fork barriers or Ter sites located within the ribosomal DNA (rDNA) intergenic spacer regions during unperturbed DNA replication. The rDNA intergenic spacer of the fission yeast Schizosaccharomyces pombe contains four polar or orientation-specific fork barriers, Ter1-3 and RFP4. Whereas the transcription terminator Reb1p binds Ter2 and Ter3 to arrest replication, the factor(s) responsible for fork arrest at Ter1 and RFP4 remain unknown. Using linker scanning mutagenesis, we have narrowed down minimal Ter1 to 21 bp. Sequence analysis revealed the presence of a consensus binding motif for the essential switch-activating and genome-stabilizing protein Sap1p within this region. Recombinant Sap1p bound Ter1 with high specificity, and endogenous Ter1 binding activity contained Sap1p and comigrated with the Sap1p-Ter1 complex. Circular permutation analysis suggested that Sap1p bends Ter1 and SAS1 upon binding. Targeted mutational analysis revealed that Ter1 mutations, which prevent Sap1p binding in vitro, are defective for replication fork arrest in vivo, whereas mutations that do not affect Sap1p binding remain competent to arrest replication. The results confirm the hypothesis that the chromatin organizer Sap1p binds site-specifically to genomic regions other than SAS1 and support the notion that Sap1p binds the rDNA fork barrier Ter1 to cause polar replication fork arrest at this site but not at SAS1.
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Affiliation(s)
- Gregor Krings
- Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, South Carolina 29425, USA
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33
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Abstract
While collisions between replication and transcription in bacteria are deemed inevitable, the fine details of the interplay between the two machineries are poorly understood. In this study, we evaluate the effects of transcription on the replication fork progression in vivo, by using electrophoresis analysis of replication intermediates. Studying Escherichia coli plasmids, which carry constitutive or inducible promoters in different orientations relative to the replication origin, we show that the mutual orientation of the two processes determines their mode of interaction. Replication elongation appears not to be affected by transcription proceeding in the codirectional orientation. Head-on transcription, by contrast, leads to severe inhibition of the replication fork progression. Furthermore, we evaluate the mechanism of this inhibition by limiting the area of direct contact between the two machineries. We observe that replication pausing zones coincide exactly with transcribed DNA segments. We conclude, therefore, that the replication fork is most likely attenuated upon direct physical interaction with the head-on transcription machinery.
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Affiliation(s)
- Ekaterina V Mirkin
- Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, 900 S. Ashland Ave., Chicago, IL 60607, USA.
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34
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Sánchez-Gorostiaga A, López-Estraño C, Krimer DB, Schvartzman JB, Hernández P. Transcription termination factor reb1p causes two replication fork barriers at its cognate sites in fission yeast ribosomal DNA in vivo. Mol Cell Biol 2004; 24:398-406. [PMID: 14673172 PMCID: PMC303360 DOI: 10.1128/mcb.24.1.398-406.2004] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Polar replication fork barriers (RFBs) near the 3' end of the rRNA transcriptional unit are a conserved feature of ribosomal DNA (rDNA) replication in eukaryotes. In the mouse, in vivo studies indicate that the cis-acting Sal boxes required for rRNA transcription termination are also involved in replication fork blockage. On the contrary, in the budding yeast Saccharomyces cerevisiae, the rRNA transcription termination factors are not required for RFBs. Here we characterized the rDNA RFBs in the fission yeast Schizosaccharomyces pombe. S. pombe rDNA contains three closely spaced polar replication barriers named RFB1, RFB2, and RFB3 in the 3' to 5' order. The transcription termination protein reb1 and its two binding sites, present at the 3' end of the coding region, were required for fork arrest at RFB2 and RFB3 in vivo. On the other hand, fork arrest at the strongest RFB1 barrier was independent of the above transcription termination factors. Therefore, RFB2 and RFB3 resemble the barriers present in the mouse rDNA, whereas RFB1 is similar to the budding yeast RFBs. These results suggest that during evolution, cis- and trans-acting factors required for rRNA transcription termination became involved in replication fork blockage also. S. pombe is suggested to be a transitional species in which both mechanisms coexist.
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Affiliation(s)
- Alicia Sánchez-Gorostiaga
- Departamento de Biología Celular y del Desarrollo, Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, 28040 Madrid, Spain
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35
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Brylawski BP, Cohen SM, Horne H, Irani N, Cordeiro-Stone M, Kaufman DG. Transitions in replication timing in a 340 kb region of human chromosomal R-Band 1p36.1. J Cell Biochem 2004; 92:755-69. [PMID: 15211573 DOI: 10.1002/jcb.20101] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
DNA replication is initiated within a few chromosomal bands as normal human fibroblasts enter the S phase. In the present study, we determined the timing of replication of sequences along a 340 kb region in one of these bands, 1p36.13, an R band on chromosome 1. Within this region, we identified a segment of DNA (approximately 140 kb) that is replicated in the first hour of the S phase and is flanked by segments replicated 1-2 h later. Using a quantitative PCR-based assay to measure sequence abundance in size-fractionated (900-1,700 nt) nascent DNA, we mapped two functional origins of replication separated by 54 kb and firing 1 h apart. One origin was found to be functional during the first hour of S and was located within a CpG island associated with a predicted gene of unknown function (Genscan NT_004610.2). The second origin was activated in the second hour of S and was mapped to a CpG island near the promoter of the aldehyde dehydrogenase 4A1 (ALDH4A1) gene. At the opposite end of the early replicating segment, a more gradual change in replication timing was observed within the span of approximately 100 kb. These data suggest that DNA replication in adjacent segments of band 1p36.13 is organized differently, perhaps in terms of replicon number and length, or rate of fork progression. In the transition areas that mark the boundaries between different temporal domains, the replication forks initiated in the early replicated region are likely to pause or delay progression before replication of the 340 kb contig is completed.
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Affiliation(s)
- Bruna P Brylawski
- Department of Pathology and Laboratory Medicine, University of North Carolina, Chapel Hill, North Carolina 27599-7525, USA
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36
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Mohanty BK, Bastia D. Binding of the replication terminator protein Fob1p to the Ter sites of yeast causes polar fork arrest. J Biol Chem 2003; 279:1932-41. [PMID: 14576157 DOI: 10.1074/jbc.m309078200] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Fob1p protein has been implicated in the termination of replication forks at the two tandem termini present in the non-transcribed spacer region located between the sequences encoding the 35 S and the 5 S RNAs of Saccharomyces cerevisiae. However, the biochemistry and mode of action of this protein were previously unknown. We have purified the Fob1p protein to near-homogeneity, and we developed a novel technique to show that it binds specifically to the Ter1 and Ter2 sequences. Interestingly, the two sequences share no detectable homology. We present two lines of evidence showing that the interaction of the Fob1p with the Ter sites causes replication termination. First, a mutant of FOB1, L104S, that significantly reduced the binding of the mutant form of the protein to the tandem Ter sites, also failed to promote replication termination in vivo. The mutant did not diminish nucleolar transport, and interaction of the mutant form of Fob1p with itself and with another protein encoded in the locus YDR026C suggested that the mutation did not cause global misfolding of the protein. Second, DNA site mutations in the Ter sequences that separately and specifically abolished replication fork arrest at Ter1 or Ter2 also eliminated sequence-specific binding of the Fob1p to the two sites. The work presented here definitively established Ter DNA-Fob1p interaction as an important step in fork arrest.
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Affiliation(s)
- Bidyut K Mohanty
- Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC 29425, USA
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37
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Codlin S, Dalgaard JZ. Complex mechanism of site-specific DNA replication termination in fission yeast. EMBO J 2003; 22:3431-40. [PMID: 12840005 PMCID: PMC165654 DOI: 10.1093/emboj/cdg330] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
A site-specific replication terminator, RTS1, is present at the Schizosaccharomyces pombe mating-type locus mat1. RTS1 regulates the direction of replication at mat1, optimizing mating-type switching that occurs as a replication-coupled recombination event. Here we show that RTS1 contains two cis-acting sequences that cooperate for efficient replication termination. First, a sequence of approximately 450 bp containing four repeated 55 bp motifs is essential for function. Secondly, a purine-rich sequence of approximately 60 bp without intrinsic activity, located proximal to the repeats, acts cooperatively to increase barrier activity 4-fold. Our data suggest that the trans-acting factors rtf1p and rtf2p act through the repeated motifs and the purine-rich element, respectively. Thus, efficient site-specific replication termination at RTS1 occurs by a complex mechanism involving several cis-acting sequences and trans-acting factors. Interestingly, RTS1 displays similarities to mammalian rDNA replication barriers.
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Affiliation(s)
- Sandra Codlin
- Marie Curie Research Institute, The Chart, Oxted, Surrey RH8 0TL, UK
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38
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Chen Y, Zhao M, Li ZP, He ML. The function of the nuclear matrix attachment region of silkworm rDNA as an autonomously replicating sequence in plasmid and chromosomal replication origin in yeast. Biochem Biophys Res Commun 2002; 299:723-9. [PMID: 12470638 DOI: 10.1016/s0006-291x(02)02746-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Nuclear matrix attachment regions (MARs) play a crucial role in chromatin architecture, gene expression, and DNA replication. Although it is well known that yeast autonomously replicating sequences (ARSs) bind nuclear matrix and MARs also function as ARS elements in yeast, whether a heterologous MAR or ARS element acts as a replication origin in the chromosome has not been elucidated. We previously identified a MAR (rMAR) located in the nontranscribed spacer (NTS) of silkworm Attacus ricini rDNA. We report here that this rMAR contains 10 copies of ARS consensus sequence (ACS) and several DNA unwinding regions. The rMAR employs ARS activity in yeast and a rARS element locates in the 3(') region of the rMAR. Furthermore, we have also revealed that either the rMAR or the rARS element functions as a replication origin in the chromosome. Our results provide the first direct evidence to demonstrate that heterologous rMAR and rARS display chromosomal origin activity, suggesting that the chromosome structure and replication origin of rDNA reserve some common features during evolution.
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Affiliation(s)
- Ying Chen
- The Institute of Molecular Biology, The University of Hong Kong, Hong Kong
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39
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Ivessa AS, Zakian VA. To fire or not to fire: origin activation in Saccharomyces cerevisiae ribosomal DNA. Genes Dev 2002; 16:2459-64. [PMID: 12368256 DOI: 10.1101/gad.1033702] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Affiliation(s)
- Andreas S Ivessa
- Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544-1014, USA
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40
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Olavarrieta L, Hernández P, Krimer DB, Schvartzman JB. DNA knotting caused by head-on collision of transcription and replication. J Mol Biol 2002; 322:1-6. [PMID: 12215409 DOI: 10.1016/s0022-2836(02)00740-4] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Collision of transcription and replication is uncommon, but the reason for nature to avoid this type of collision is still poorly understood. In Escherichia coli pBR322 is unstable and rapidly lost without selective pressure. Stability can be rescued if transcription of the tetracycline-resistance gene (Tet(R)), progressing against replication, is avoided. We investigated the topological consequences of the collision of transcription and replication in pBR322-derived plasmids where head-on collision between the replication fork and the RNA polymerase transcribing the Tet(R) gene was allowed or avoided. The results obtained indicate that this type of collision triggers knotting of the daughter duplexes behind the fork. We propose this deleterious topological consequence could explain the instability of pBR322 and could be also one of the reasons for nature to avoid head-on collision of transcription and replication.
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MESH Headings
- Autoradiography
- Comet Assay
- DNA Replication
- DNA, Bacterial/biosynthesis
- DNA, Bacterial/chemistry
- DNA, Bacterial/genetics
- DNA, Bacterial/metabolism
- DNA, Superhelical/biosynthesis
- DNA, Superhelical/chemistry
- DNA, Superhelical/genetics
- DNA, Superhelical/metabolism
- DNA-Directed RNA Polymerases/metabolism
- Escherichia coli/enzymology
- Escherichia coli/genetics
- Genes, Bacterial/genetics
- Models, Genetic
- Nucleic Acid Conformation
- Plasmids/biosynthesis
- Plasmids/chemistry
- Plasmids/genetics
- Plasmids/metabolism
- Tetracycline Resistance/genetics
- Transcription, Genetic
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Affiliation(s)
- L Olavarrieta
- Departamento de Biología, Celular y del Desarrollo, Centro de Investigaciones Biológicas (CSIC), Velázquez 144, 28006 Madrid, Spain
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41
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Wallisch M, Kunkel E, Hoehn K, Grummt F. Ku antigen supports termination of mammalian rDNA replication by transcription termination factor TTF-I. Biol Chem 2002; 383:765-71. [PMID: 12108541 DOI: 10.1515/bc.2002.080] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
A replication fork barrier at the 3'-end of mouse ribosomal RNA genes blocks bidirectional fork progression and limits DNA replication to the same direction as transcription. This barrier is an inherent property of a defined DNA-protein complex including transcription termination factor I, and specific protein-protein interactions occur between this factor and protein(s) of the replication machinery. Here we report that a second DNA-binding protein is essential for barrier activity. We have purified and functionally characterised the protein from HeLa cells. The final preparation contained two polypeptides with molecular masses of 70 and 86 kDa, respectively. Both polypeptides interact with a GC-stretch adjacent to the binding site of transcription termination factor I. The specificity of binding to the barrier DNA was demonstrated in an electrophoretic mobility shift assay. The biochemical properties of this protein resemble that of Ku antigen, a human nuclear DNA-binding heterodimer that is the target of autoimmune-antibodies in several autoimmune diseases. Recombinant Ku protein, purified as heterodimer from co-infected insect cells, is able to partially rescue the barrier activity in Ku-depleted HeLa cell extracts. These data demonstrate that transcription termination factor I and Ku act synergistically to prevent head-on collision between the replication and the transcription machinery.
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42
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Putter V, Grummt F. Transcription termination factor TTF-I exhibits contrahelicase activity during DNA replication. EMBO Rep 2002; 3:147-52. [PMID: 11818337 PMCID: PMC1083968 DOI: 10.1093/embo-reports/kvf027] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
In mammals, sequence-specific termination of DNA replication within the ribosomal RNA genes is catalyzed by a defined DNA-protein complex that includes transcription termination factor I (TTF-I). Here we show that TTF-I acts as a polar contrahelicase contrary to the intrinsic 3' -->5' helicase activity of SV40 large T antigen. The contrahelicase activity requires binding of TTF-I to its cognate recognition site and the presence of an auxiliary GC-rich sequence, which is able to form a specific secondary structure. Mutations in the GC-rich sequence lead to a loss of folding into correct secondary structure and abrogate contrahelicase activity. The finding suggests that a specific interaction between the Sal box-bound TTF-I and the GC-rich sequence is essential for the inhibition of T antigen helicase. Analyses of N-terminally truncated mutants of TTF-I showed inhibition of helicase by the same domain of TTF-I, which is also responsible for replication fork arrest.
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Affiliation(s)
- Vera Putter
- Institute of Biochemistry, University of Würzburg, D-97074 Würzburg, Germany
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43
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Abstract
DNA helicases are required for DNA replication, recombination and repair. Despite a common enzymatic function - the ability to unwind duplex DNA - most helicases share only limited amino acid sequence similarity. Helicases that have significant sequence similarity define a subfamily. It remains unclear, however, how this sequence similarity relates to helicase function. The Saccharomyces cerevisiae Pif1p helicase is the prototype member of a helicase subfamily that is conserved from yeasts to humans. As the two Pif1p subfamily members studied to date affect the same DNA sequences, the amino acid similarity that defines this subfamily might reflect common substrates.
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Affiliation(s)
- J B Bessler
- Dept of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
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44
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Gruber M, Wellinger RE, Sogo JM. Architecture of the replication fork stalled at the 3' end of yeast ribosomal genes. Mol Cell Biol 2000; 20:5777-87. [PMID: 10891513 PMCID: PMC86055 DOI: 10.1128/mcb.20.15.5777-5787.2000] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Every unit of the rRNA gene cluster of Saccharomyces cerevisiae contains a unique site, termed the replication fork barrier (RFB), where progressing replication forks are stalled in a polar manner. In this work, we determined the positions of the nascent strands at the RFB at nucleotide resolution. Within an HpaI-HindIII fragment essential for the RFB, a major and two closely spaced minor arrest sites were found. In the majority of molecules, the stalled lagging strand was completely processed and the discontinuously synthesized nascent lagging strand was extended three bases farther than the continuously synthesized leading strand. A model explaining these findings is presented. Our analysis included for the first time the use of T4 endonuclease VII, an enzyme recognizing branched DNA molecules. This enzyme cleaved predominantly in the newly synthesized homologous arms, thereby specifically releasing the leading arm.
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Affiliation(s)
- M Gruber
- Institute of Cell Biology, ETH Hönggerberg, CH-8093 Zürich, Switzerland
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45
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Ward TR, Hoang ML, Prusty R, Lau CK, Keil RL, Fangman WL, Brewer BJ. Ribosomal DNA replication fork barrier and HOT1 recombination hot spot: shared sequences but independent activities. Mol Cell Biol 2000; 20:4948-57. [PMID: 10848619 PMCID: PMC85945 DOI: 10.1128/mcb.20.13.4948-4957.2000] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
In the ribosomal DNA of Saccharomyces cerevisiae, sequences in the nontranscribed spacer 3' of the 35S ribosomal RNA gene are important to the polar arrest of replication forks at a site called the replication fork barrier (RFB) and also to the cis-acting, mitotic hyperrecombination site called HOT1. We have found that the RFB and HOT1 activity share some but not all of their essential sequences. Many of the mutations that reduce HOT1 recombination also decrease or eliminate fork arrest at one of two closely spaced RFB sites, RFB1 and RFB2. A simple model for the juxtaposition of RFB and HOT1 sequences is that the breakage of strands in replication forks arrested at RFB stimulates recombination. Contrary to this model, we show here that HOT1-stimulated recombination does not require the arrest of forks at the RFB. Therefore, while HOT1 activity is independent of replication fork arrest, HOT1 and RFB require some common sequences, suggesting the existence of a common trans-acting factor(s).
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Affiliation(s)
- T R Ward
- Department of Genetics, University of Washington, Seattle 98195, USA
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46
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Ivessa AS, Zhou JQ, Zakian VA. The Saccharomyces Pif1p DNA helicase and the highly related Rrm3p have opposite effects on replication fork progression in ribosomal DNA. Cell 2000; 100:479-89. [PMID: 10693764 DOI: 10.1016/s0092-8674(00)80683-2] [Citation(s) in RCA: 230] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Replication of Saccharomyces ribosomal DNA (rDNA) proceeds bidirectionally from origins in a subset of the approximately 150 tandem repeats, but the leftward-moving fork stops when it encounters the replication fork barrier (RFB). The Pif1p helicase and the highly related Rrm3p were rDNA associated in vivo. Both proteins affected rDNA replication but had opposing effects on fork progression. Pif1p helped maintain the RFB. Rrm3p appears to be the replicative helicase for rDNA as it acted catalytically to promote fork progression throughout the rDNA. Loss of Rrm3p increased rDNA breakage and accumulation of rDNA circles, whereas breakage and circles were less common in pif1 cells. These data support a model in which replication fork pausing causes breakage and recombination in the rDNA.
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Affiliation(s)
- A S Ivessa
- Department of Molecular Biology, Princeton University, New Jersey 08544-1014, USA
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47
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Viguera E, Hernández P, Krimer DB, Lurz R, Schvartzman JB. Visualisation of plasmid replication intermediates containing reversed forks. Nucleic Acids Res 2000; 28:498-503. [PMID: 10606648 PMCID: PMC102505 DOI: 10.1093/nar/28.2.498] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Blockage of replication forks can have deleterious consequences for the cell as it may prompt premature termination of DNA replication. Moreover, the blocked replication intermediate (RI) could be particularly sensitive to recombination processes. We analysed the different populations of RIs generated in vivo in the bacterial plasmid pPI21 after pausing of replication forks at the inversely oriented ColE1 origin. To achieve this goal, a new method was developed based on two-dimensional agarose gel electrophoresis. This method allows the isolation of specific RIs, even when they were rather scarce, from the total DNA. Here we describe the occurrence of RI restriction fragments containing reversed forks. These Holliday-like structures have been postulated but never observed before.
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Affiliation(s)
- E Viguera
- Departamento de Biología Celular y del Desarrollo, CIB (CSIC), Velázquez 144, 28006 Madrid, Spain
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48
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Abstract
Chromosome replication is not a uniform and continuous process. Replication forks can be slowed down or arrested by DNA secondary structures, specific protein-DNA complexes, specific DNA-RNA hybrids, or interactions between the replication and transcription machineries. Replication arrest has important implications for the topology of replication intermediates and can trigger homologous and illegitimate recombination. Thus, replication arrest may be a key factor in genome instability. Several examples of these phenomena are reviewed here.
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Affiliation(s)
- O Hyrien
- Ecole Normale Supérieure, Paris, France
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49
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Rothstein R, Michel B, Gangloff S. Replication fork pausing and recombination or “gimme a break”. Genes Dev 2000. [DOI: 10.1101/gad.14.1.1] [Citation(s) in RCA: 126] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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50
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Maric C, Levacher B, Hyrien O. Developmental regulation of replication fork pausing in Xenopus laevis ribosomal RNA genes. J Mol Biol 1999; 291:775-88. [PMID: 10452888 DOI: 10.1006/jmbi.1999.3017] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In early Xenopus embryos, replication forks move along the rRNA genes (rDNA) at a uniform rate and terminate at multiple, apparently random sites. In contrast, a polar replication fork barrier (RFB) is found at the 3' end of the rRNA genes in Xenopus cultured cells. We have now analysed the replication intermediates of Xenopus rDNA from a wide range of developmental stages by 2D gel electrophoresis. Surprisingly, up to 15 different replication fork pausing sites (RFPs) simultaneously appear in the rDNA at the midgastrula stage, when rRNA transcription abruptly increases. They disappear during the neurula stage, except for a polar RFP at the 3' end of Xthe transcription unit, which persists to the tadpole stage. The latter RFP is found at the same location as the RFB in cultured cells; however the arrest of replication forks at this RFP is not absolute, since termination occurs at multiple positions throughout the rDNA repeat. The efficiency of fork arrest at this RFP remains constant from midgastrula to early tadpole, and decreases around hatching. The transient appearance of multiple RFPs at midgastrula may reflect some chromatin remodeling associated with developmental activation of rRNA transcription.
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Affiliation(s)
- C Maric
- Laboratoire de Génétique Moléculaire, Ecole Normale Supérieure, 46 rue d'Ulm, Paris Cedex 05, 75230, France
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