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Gupta SV, Campos L, Schmidt KH. Mitochondrial superoxide dismutase Sod2 suppresses nuclear genome instability during oxidative stress. Genetics 2023; 225:iyad147. [PMID: 37638880 PMCID: PMC10550321 DOI: 10.1093/genetics/iyad147] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2023] [Accepted: 07/14/2023] [Indexed: 08/29/2023] Open
Abstract
Oxidative stress can damage DNA and thereby contribute to genome instability. To avoid an imbalance or overaccumulation of reactive oxygen species (ROS), cells are equipped with antioxidant enzymes that scavenge excess ROS. Cells lacking the RecQ-family DNA helicase Sgs1, which contributes to homology-dependent DNA break repair and chromosome stability, are known to accumulate ROS, but the origin and consequences of this oxidative stress phenotype are not fully understood. Here, we show that the sgs1 mutant exhibits elevated mitochondrial superoxide, increased mitochondrial mass, and accumulation of recombinogenic DNA lesions that can be suppressed by antioxidants. Increased mitochondrial mass in the sgs1Δ mutant is accompanied by increased mitochondrial branching, which was also inducible in wildtype cells by replication stress. Superoxide dismutase Sod2 genetically interacts with Sgs1 in the suppression of nuclear chromosomal rearrangements under paraquat (PQ)-induced oxidative stress. PQ-induced chromosome rearrangements in the absence of Sod2 are promoted by Rad51 recombinase and the polymerase subunit Pol32. Finally, the dependence of chromosomal rearrangements on the Rev1/Pol ζ mutasome suggests that under oxidative stress successful DNA synthesis during DNA break repair depends on translesion DNA synthesis.
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Affiliation(s)
- Sonia Vidushi Gupta
- Department of Molecular Biosciences, University of South Florida, 4202 East Fowler Avenue, Tampa, FL 33620, USA
| | - Lillian Campos
- Department of Molecular Biosciences, University of South Florida, 4202 East Fowler Avenue, Tampa, FL 33620, USA
| | - Kristina Hildegard Schmidt
- Department of Molecular Biosciences, University of South Florida, 4202 East Fowler Avenue, Tampa, FL 33620, USA
- Cancer Biology and Evolution Program, H. Lee Moffitt Cancer Center and Research Institute, 12902 USF Magnolia Drive, Tampa, FL 33612, USA
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2
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Le ST, Choi S, Lee SW, Kim H, Ahn B. ssDNA reeling is an intermediate step in the reiterative DNA unwinding activity of the WRN-1 helicase. J Biol Chem 2023; 299:105081. [PMID: 37495105 PMCID: PMC10480542 DOI: 10.1016/j.jbc.2023.105081] [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: 01/26/2023] [Revised: 07/14/2023] [Accepted: 07/14/2023] [Indexed: 07/28/2023] Open
Abstract
RecQ helicases are highly conserved between bacteria and humans. These helicases unwind various DNA structures in the 3' to 5'. Defective helicase activity elevates genomic instability and is associated with predisposition to cancer and/or premature aging. Recent single-molecule analyses have revealed the repetitive unwinding behavior of RecQ helicases from Escherichia coli to humans. However, the detailed mechanisms underlying this behavior are unclear. Here, we performed single-molecule studies of WRN-1 Caenorhabditis elegans RecQ helicase on various DNA constructs and characterized WRN-1 unwinding dynamics. We showed that WRN-1 persistently repeated cycles of DNA unwinding and rewinding with an unwinding limit of 25 to 31 bp per cycle. Furthermore, by monitoring the ends of the displaced strand during DNA unwinding we demonstrated that WRN-1 reels in the ssDNA overhang in an ATP-dependent manner. While WRN-1 reeling activity was inhibited by a C. elegans homolog of human replication protein A, we found that C. elegans replication protein A actually switched the reiterative unwinding activity of WRN-1 to unidirectional unwinding. These results reveal that reeling-in ssDNA is an intermediate step in the reiterative unwinding process for WRN-1 (i.e., the process proceeds via unwinding-reeling-rewinding). We propose that the reiterative unwinding activity of WRN-1 may prevent extensive unwinding, allow time for partner proteins to assemble on the active region, and permit additional modulation in vivo.
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Affiliation(s)
- Son Truong Le
- Department of Life Sciences, University of Ulsan, Ulsan, Republic of Korea
| | - Seoyun Choi
- Department of Biochemistry & Molecular Medicine, School of Medicine & Health Sciences, The George Washington University, Washington DC, USA
| | - Seung-Won Lee
- Department of Biomedical Engineering, Ulsan National Institute of Science and Technology, Ulsan, Republic of Korea
| | - Hajin Kim
- Department of Biomedical Engineering, Ulsan National Institute of Science and Technology, Ulsan, Republic of Korea; Center for Genomic Integrity, Institute for Basic Science, Ulsan, Republic of Korea.
| | - Byungchan Ahn
- Department of Life Sciences, University of Ulsan, Ulsan, Republic of Korea.
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3
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Calvo PA, Mateo-Cáceres V, Díaz-Arco S, Redrejo-Rodríguez M, de Vega M. The enterohemorrhagic Escherichia coli insertion sequence-excision enhancer protein is a DNA polymerase with microhomology-mediated end-joining activity. Nucleic Acids Res 2023; 51:1189-1207. [PMID: 36715333 PMCID: PMC9943667 DOI: 10.1093/nar/gkad017] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2022] [Revised: 12/30/2022] [Accepted: 01/05/2023] [Indexed: 01/31/2023] Open
Abstract
Bacterial genomes contain an abundance of transposable insertion sequence (IS) elements that are essential for genome evolution and fitness. Among them, IS629 is present in most strains of enterohemorrhagic Escherichia coli O157 and accounts for many polymorphisms associated with gene inactivation and/or genomic deletions. The excision of IS629 from the genome is promoted by IS-excision enhancer (IEE) protein. Despite IEE has been identified in the most pathogenic serotypes of E. coli, its biochemical features that could explain its role in IS excision are not yet understood. We show that IEE is present in >30% of all available E. coli genome assemblies, and is highly conserved and very abundant within enterohemorrhagic, enteropathogenic and enterotoxigenic genomes. In vitro analysis of the recombinant protein from E. coli O157:H7 revealed the presence of a Mn2+-dependent error-prone DNA polymerase activity in its N-terminal archaeo-eukaryotic primase (AEP) domain able to promote dislocations of the primer and template strands. Importantly, IEE could efficiently perform in vitro an end-joining reaction of 3'-single-strand DNA overhangs with ≥4 bp of homology requiring both the N-terminal AEP and C-terminal helicase domains. The proposed role for IEE in the novel IS excision mechanism is discussed.
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Affiliation(s)
- Patricia A Calvo
- Centro de Biología Molecular Severo Ochoa (Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid), Nicolás Cabrera 1, Madrid 28049, Spain
| | - Víctor Mateo-Cáceres
- Department of Biochemistry, School of Medicine, Universidad Autónoma de Madrid and Instituto de Investigaciones Biomédicas Alberto Sols (Universidad Autónoma de Madrid-Consejo Superior de Investigaciones Científicas), Madrid, Spain
| | - Silvia Díaz-Arco
- Centro de Biología Molecular Severo Ochoa (Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid), Nicolás Cabrera 1, Madrid 28049, Spain
| | - Modesto Redrejo-Rodríguez
- Department of Biochemistry, School of Medicine, Universidad Autónoma de Madrid and Instituto de Investigaciones Biomédicas Alberto Sols (Universidad Autónoma de Madrid-Consejo Superior de Investigaciones Científicas), Madrid, Spain
| | - Miguel de Vega
- To whom correspondence should be addressed. Tel: +34 911964717; Fax: +34 911964420;
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4
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Choi S, Lee SW, Kim H, Ahn B. Molecular characteristics of reiterative DNA unwinding by the Caenorhabditis elegans RecQ helicase. Nucleic Acids Res 2019; 47:9708-9720. [PMID: 31435650 PMCID: PMC6765134 DOI: 10.1093/nar/gkz708] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2019] [Revised: 07/31/2019] [Accepted: 08/13/2019] [Indexed: 12/31/2022] Open
Abstract
The RecQ family of helicases is highly conserved both structurally and functionally from bacteria to humans. Defects in human RecQ helicases are associated with genetic diseases that are characterized by cancer predisposition and/or premature aging. RecQ proteins exhibit 3'-5' helicase activity and play critical roles in genome maintenance. Recent advances in single-molecule techniques have revealed the reiterative unwinding behavior of RecQ helicases. However, the molecular mechanisms involved in this process remain unclear, with contradicting reports. Here, we characterized the unwinding dynamics of the Caenorhabditis elegans RecQ helicase HIM-6 using single-molecule fluorescence resonance energy transfer measurements. We found that HIM-6 exhibits reiterative DNA unwinding and the length of DNA unwound by the helicase is sharply defined at 25-31 bp. Experiments using various DNA substrates revealed that HIM-6 utilizes the mode of 'sliding back' on the translocated strand, without strand-switching for rewinding. Furthermore, we found that Caenorhabditis elegans replication protein A, a single-stranded DNA binding protein, suppresses the reiterative behavior of HIM-6 and induces unidirectional, processive unwinding, possibly through a direct interaction between the proteins. Our findings shed new light on the mechanism of DNA unwinding by RecQ family helicases and their co-operation with RPA in processing DNA.
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Affiliation(s)
- Seoyun Choi
- Department of Life Sciences, University of Ulsan, Ulsan 44610, Republic of Korea
| | - Seung-Won Lee
- School of Life Sciences, Ulsan National Institute of Science and Technology, Ulsan 44610, Republic of Korea
| | - Hajin Kim
- School of Life Sciences, Ulsan National Institute of Science and Technology, Ulsan 44610, Republic of Korea.,Center for Genomic Integrity, Institute for Basic Science, Ulsan 44610, Republic of Korea
| | - Byungchan Ahn
- Department of Life Sciences, University of Ulsan, Ulsan 44610, Republic of Korea
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5
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Cox RL, Hofley CM, Tatapudy P, Patel RK, Dayani Y, Betcher M, LaRocque JR. Functional conservation of RecQ helicase BLM between humans and Drosophila melanogaster. Sci Rep 2019; 9:17527. [PMID: 31772289 PMCID: PMC6879748 DOI: 10.1038/s41598-019-54101-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2019] [Accepted: 11/09/2019] [Indexed: 12/02/2022] Open
Abstract
RecQ helicases are a family of proteins involved in maintaining genome integrity with functions in DNA repair, recombination, and replication. The human RecQ helicase family consists of five helicases: BLM, WRN, RECQL, RECQL4, and RECQL5. Inherited mutations in RecQ helicases result in Bloom Syndrome (BLM mutation), Werner Syndrome (WRN mutation), Rothmund-Thomson Syndrome (RECQL4 mutation), and other genetic diseases, including cancer. The RecQ helicase family is evolutionarily conserved, as Drosophila melanogaster have three family members: DmBlm, DmRecQL4, and DmRecQL5 and DmWRNexo, which contains a conserved exonuclease domain. DmBlm has functional similarities to human BLM (hBLM) as mutants demonstrate increased sensitivity to ionizing radiation (IR) and a decrease in DNA double-strand break (DSB) repair. To determine the extent of functional conservation of RecQ helicases, hBLM was expressed in Drosophila using the GAL4 > UASp system to determine if GAL4 > UASp::hBLM can rescue DmBlm mutant sensitivity to IR. hBLM was able to rescue female DmBlm mutant sensitivity to IR, supporting functional conservation. This functional conservation is specific to BLM, as human GAL4 > UASp::RECQL was not able to rescue DmBlm mutant sensitivity to IR. These results demonstrate the conserved role of BLM in maintaining the genome while reinforcing the applicability of using Drosophila as a model system to study Bloom Syndrome.
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Affiliation(s)
- Rebecca L Cox
- Department of Human Science, Georgetown University Medical Center, Washington, DC, 20057, USA
| | - Carolyn M Hofley
- Department of Human Science, Georgetown University Medical Center, Washington, DC, 20057, USA
| | - Pallavi Tatapudy
- Department of Human Science, Georgetown University Medical Center, Washington, DC, 20057, USA
| | - Romil K Patel
- Department of Human Science, Georgetown University Medical Center, Washington, DC, 20057, USA
| | - Yaron Dayani
- Department of Human Science, Georgetown University Medical Center, Washington, DC, 20057, USA
| | - Madison Betcher
- Department of Human Science, Georgetown University Medical Center, Washington, DC, 20057, USA
| | - Jeannine R LaRocque
- Department of Human Science, Georgetown University Medical Center, Washington, DC, 20057, USA.
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6
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Studying Werner syndrome to elucidate mechanisms and therapeutics of human aging and age-related diseases. Biogerontology 2019; 20:255-269. [PMID: 30666569 DOI: 10.1007/s10522-019-09798-2] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2018] [Accepted: 01/17/2019] [Indexed: 01/22/2023]
Abstract
Aging is a natural and unavoidable part of life. However, aging is also the primary driver of the dominant human diseases, such as cardiovascular disease, cancer, and neurodegenerative diseases, including Alzheimer's disease. Unraveling the sophisticated molecular mechanisms of the human aging process may provide novel strategies to extend 'healthy aging' and the cure of human aging-related diseases. Werner syndrome (WS), is a heritable human premature aging disease caused by mutations in the gene encoding the Werner (WRN) DNA helicase. As a classical premature aging disease, etiological exploration of WS can shed light on the mechanisms of normal human aging and facilitate the development of interventional strategies to improve healthspan. Here, we summarize the latest progress of the molecular understandings of WRN protein, highlight the advantages of using different WS model systems, including Caenorhabditis elegans, Drosophila melanogaster and induced pluripotent stem cell (iPSC) systems. Further studies on WS will propel drug development for WS patients, and possibly also for normal age-related diseases.
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7
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High-throughput creation and functional profiling of DNA sequence variant libraries using CRISPR-Cas9 in yeast. Nat Biotechnol 2018; 36:540-546. [PMID: 29786095 PMCID: PMC5990468 DOI: 10.1038/nbt.4147] [Citation(s) in RCA: 60] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2017] [Accepted: 04/18/2018] [Indexed: 01/20/2023]
Abstract
Construction and characterization of large genetic variant libraries is essential for understanding genome function, but remains challenging. Here, we introduce a Cas9-based approach for generating pools of mutants with defined genetic alterations (deletions, substitutions, and insertions) with an efficiency of 80–100% in yeast, along with methods for tracking their fitness en masse. We demonstrate the utility of our approach by characterizing the DNA helicase SGS1 with small tiling deletion mutants that span the length of the protein and a series of point mutations against highly conserved residues in the protein. In addition, we created a genome-wide library targeting 315 poorly characterized small open reading frames (smORFs, <100 amino acids in length) scattered throughout the yeast genome, and assessed which are vital for growth under various environmental conditions. Our strategy allows fundamental biological questions to be investigated in a high-throughput manner with precision.
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8
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The Role of Blm Helicase in Homologous Recombination, Gene Conversion Tract Length, and Recombination Between Diverged Sequences in Drosophilamelanogaster. Genetics 2017; 207:923-933. [PMID: 28912341 DOI: 10.1534/genetics.117.300285] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2017] [Accepted: 09/10/2017] [Indexed: 11/18/2022] Open
Abstract
DNA double-strand breaks (DSBs) are a particularly deleterious class of DNA damage that threatens genome integrity. DSBs are repaired by three pathways: nonhomologous-end joining (NHEJ), homologous recombination (HR), and single-strand annealing (SSA). Drosophila melanogaster Blm (DmBlm) is the ortholog of Saccharomyces cerevisiae SGS1 and human BLM, and has been shown to suppress crossovers in mitotic cells and repair mitotic DNA gaps via HR. To further elucidate the role of DmBlm in repair of a simple DSB, and in particular recombination mechanisms, we utilized the Direct Repeat of white (DR-white) and Direct Repeat of whitewith mutations (DR-white.mu) repair assays in multiple mutant allele backgrounds. DmBlm null and helicase-dead mutants both demonstrated a decrease in repair by noncrossover HR, and a concurrent increase in non-HR events, possibly including SSA, crossovers, deletions, and NHEJ, although detectable processing of the ends was not significantly impacted. Interestingly, gene conversion tract lengths of HR repair events were substantially shorter in DmBlm null but not helicase-dead mutants, compared to heterozygote controls. Using DR-white.mu, we found that, in contrast to Sgs1, DmBlm is not required for suppression of recombination between diverged sequences. Taken together, our data suggest that DmBlm helicase function plays a role in HR, and the steps that contribute to determining gene conversion tract length are helicase-independent.
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9
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Effect of Low Doses (5-40 cGy) of Gamma-irradiation on Lifespan and Stress-related Genes Expression Profile in Drosophila melanogaster. PLoS One 2015; 10:e0133840. [PMID: 26248317 PMCID: PMC4527671 DOI: 10.1371/journal.pone.0133840] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2015] [Accepted: 07/03/2015] [Indexed: 02/04/2023] Open
Abstract
Studying of the effects of low doses of γ-irradiation is a crucial issue in different areas of interest, from environmental safety and industrial monitoring to aerospace and medicine. The goal of this work is to identify changes of lifespan and expression stress-sensitive genes in Drosophila melanogaster, exposed to low doses of γ-irradiation (5 – 40 cGy) on the imaginal stage of development. Although some changes in life extensity in males were identified (the effect of hormesis after the exposure to 5, 10 and 40 cGy) as well as in females (the effect of hormesis after the exposure to 5 and 40 cGy), they were not caused by the organism “physiological” changes. This means that the observed changes in life expectancy are not related to the changes of organism physiological functions after the exposure to low doses of ionizing radiation. The identified changes in gene expression are not dose-dependent, there is not any proportionality between dose and its impact on expression. These results reflect nonlinear effects of low dose radiation and sex-specific radio-resistance of the postmitotic cell state of Drosophila melanogaster imago.
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Jung H, Lee JA, Choi S, Lee H, Ahn B. Characterization of the Caenorhabditis elegans HIM-6/BLM helicase: unwinding recombination intermediates. PLoS One 2014; 9:e102402. [PMID: 25036527 PMCID: PMC4103807 DOI: 10.1371/journal.pone.0102402] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2014] [Accepted: 06/12/2014] [Indexed: 02/02/2023] Open
Abstract
Mutations in three human RecQ genes are implicated in heritable human syndromes. Mutations in BLM, a RecQ gene, cause Bloom syndrome (BS), which is characterized by short stature, cancer predisposition, and sensitivity to sunlight. BLM is a RecQ DNA helicase that, with interacting proteins, is able to dissolve various DNA structures including double Holliday junctions. A BLM ortholog, him-6, has been identified in Caenorhabditis elegans, but little is known about its enzymatic activities or its in vivo roles. By purifying recombinant HIM-6 and performing biochemical assays, we determined that the HIM-6 has DNA-dependent ATPase activity HIM-6 and helicase activity that proceeds in the 3'-5' direction and needs at least five 3' overhanging nucleotides. HIM-6 is also able to unwind DNA structures including D-loops and Holliday junctions. Worms with him-6 mutations were defective in recovering the cell cycle arrest after HU treatment. These activities strongly support in vivo roles for HIM-6 in processing recombination intermediates.
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Affiliation(s)
- Hana Jung
- Department of Life Sciences, University of Ulsan, Ulsan, Republic of Korea
| | - Jin A Lee
- Department of Life Sciences, University of Ulsan, Ulsan, Republic of Korea
| | - Seoyoon Choi
- Department of Life Sciences, University of Ulsan, Ulsan, Republic of Korea
| | - Hyunwoo Lee
- Department of Life Sciences, University of Ulsan, Ulsan, Republic of Korea
| | - Byungchan Ahn
- Department of Life Sciences, University of Ulsan, Ulsan, Republic of Korea
- * E-mail:
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11
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Gaivão I, Rodríguez R, Sierra LM. Use of the Comet Assay to Study DNA Repair in Drosophila melanogaster. GENOTOXICITY AND DNA REPAIR 2014. [DOI: 10.1007/978-1-4939-1068-7_23] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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12
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Gonzalez C. Drosophila melanogaster: a model and a tool to investigate malignancy and identify new therapeutics. Nat Rev Cancer 2013; 13:172-83. [PMID: 23388617 DOI: 10.1038/nrc3461] [Citation(s) in RCA: 206] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
For decades, lower-model organisms such as Drosophila melanogaster have often provided the first glimpse into the mechanism of action of human cancer-related proteins, thus making a substantial contribution to elucidating the molecular basis of the disease. More recently, D. melanogaster strains that are engineered to recapitulate key aspects of specific types of human cancer have been paving the way for the future role of this 'workhorse' of biomedical research, helping to further investigate the process of malignancy, and serving as platforms for therapeutic drug discovery.
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Affiliation(s)
- Cayetano Gonzalez
- IRB-Barcelona, c/Baldiri Reixac 10-12, Barcelona, Spain. gonzalez@ irbbarcelona.org
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13
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Rezazadeh S. On BLM helicase in recombination-mediated telomere maintenance. Mol Biol Rep 2012; 40:3049-64. [DOI: 10.1007/s11033-012-2379-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2012] [Accepted: 12/17/2012] [Indexed: 11/29/2022]
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14
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Hyun M, Park S, Kim E, Kim DH, Lee SJ, Koo HS, Seo YS, Ahn B. Physical and functional interactions of Caenorhabditis elegans WRN-1 helicase with RPA-1. Biochemistry 2012; 51:1336-45. [PMID: 22257160 DOI: 10.1021/bi200791p] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The Caenorhabditis elegans Werner syndrome protein, WRN-1, a member of the RecQ helicase family, has a 3'-5' DNA helicase activity. Worms with defective wrn-1 exhibit premature aging phenotypes and an increased level of genome instability. In response to DNA damage, WRN-1 participates in the initial stages of checkpoint activation in concert with C. elegans replication protein A (RPA-1). WRN-1 helicase is stimulated by RPA-1 on long DNA duplex substrates. However, the mechanism by which RPA-1 stimulates DNA unwinding and the function of the WRN-1-RPA-1 interaction are not clearly understood. We have found that WRN-1 physically interacts with two RPA-1 subunits, CeRPA73 and CeRPA32; however, full-length WRN-1 helicase activity is stimulated by only the CeRPA73 subunit, while the WRN-1(162-1056) fragment that harbors the helicase activity requires both the CeRPA73 and CeRPA32 subunits for the stimulation. We also found that the CeRPA73(1-464) fragment can stimulate WRN-1 helicase activity and that residues 335-464 of CeRPA73 are important for physical interaction with WRN-1. Because CeRPA73 and the CeRPA73(1-464) fragment are able to bind single-stranded DNA (ssDNA), the stimulation of WRN-1 helicase by RPA-1 is most likely due to the ssDNA binding activity of CeRPA73 and the direct interaction of WRN-1 and CeRPA73.
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Affiliation(s)
- Moonjung Hyun
- Department of Life Sciences, University of Ulsan, Ulsan 680-749, Korea
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15
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Loss of the bloom syndrome helicase increases DNA ligase 4-independent genome rearrangements and tumorigenesis in aging Drosophila. Genome Biol 2011; 12:R121. [PMID: 22183041 PMCID: PMC3334616 DOI: 10.1186/gb-2011-12-12-r121] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2011] [Revised: 11/25/2011] [Accepted: 12/19/2011] [Indexed: 12/12/2022] Open
Abstract
Background The BLM DNA helicase plays a vital role in maintaining genome stability. Mutations in BLM cause Bloom syndrome, a rare disorder associated with cancer predisposition and premature aging. Humans and mice with blm mutations have increased frequencies of spontaneous mutagenesis, but the molecular basis of this increase is not well understood. In addition, the effect of aging on spontaneous mutagenesis in blm mutants has not been characterized. To address this, we used a lacZ reporter system in wild-type and several mutant strains of Drosophila melanogaster to analyze mechanisms of mutagenesis throughout their lifespan. Results Our data show that Drosophila lacking BLM have an elevated frequency of spontaneous genome rearrangements that increases with age. Although in normal flies most genome rearrangements occur through DNA ligase 4-dependent classical end joining, most rearrangements that accumulate during aging in blm mutants do not require DNA ligase 4, suggesting the influence of an alternative end-joining mechanism. Adult blm mutants also display reduced lifespan and ligase 4-independent enhanced tumorigenesis in mitotically active tissues. Conclusions These results suggest that Drosophila BLM suppresses error-prone alternative end-joining repair of DNA double-strand breaks that can result in genome instability and tumor formation during aging. In addition, since loss of BLM significantly affects lifespan and tumorigenesis, the data provide a link between error-prone end joining, genome rearrangements, and tumor formation in a model metazoan.
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16
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Double-strand breaks in heterochromatin move outside of a dynamic HP1a domain to complete recombinational repair. Cell 2011; 144:732-44. [PMID: 21353298 DOI: 10.1016/j.cell.2011.02.012] [Citation(s) in RCA: 407] [Impact Index Per Article: 31.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2010] [Revised: 12/15/2010] [Accepted: 02/07/2011] [Indexed: 01/07/2023]
Abstract
Double-strand breaks (DSBs) in heterochromatic repetitive DNAs pose significant threats to genome integrity, but information about how such lesions are processed and repaired is sparse. We observe dramatic expansion and dynamic protrusions of the heterochromatin domain in response to ionizing radiation (IR) in Drosophila cells. We also find that heterochromatic DSBs are repaired by homologous recombination (HR) but with striking differences from euchromatin. Proteins involved in early HR events (resection) are rapidly recruited to DSBs within heterochromatin. In contrast, Rad51, which mediates strand invasion, only associates with DSBs that relocalize outside of the domain. Heterochromatin expansion and relocalization of foci require checkpoint and resection proteins. Finally, the Smc5/6 complex is enriched in heterochromatin and is required to exclude Rad51 from the domain and prevent abnormal recombination. We propose that the spatial and temporal control of DSB repair in heterochromatin safeguards genome stability by preventing aberrant exchanges between repeats.
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The adenovirus E1b55K/E4orf6 complex induces degradation of the Bloom helicase during infection. J Virol 2010; 85:1887-92. [PMID: 21123383 DOI: 10.1128/jvi.02134-10] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The adenovirus (Ad) E1b55K and E4orf6 gene products assemble an E3 ubiquitin ligase complex that promotes degradation of cellular proteins. Among the known substrates are p53 and the Mre11-Rad50-Nbs1 (MRN) complex. Since members of the RecQ helicase family function together with MRN in genome maintenance, we investigated whether adenovirus affects RecQ proteins. We show that Bloom helicase (BLM) is degraded during adenovirus type 5 (Ad5) infection. BLM degradation is mediated by E1b55K/E4orf6 but is independent of MRN. We detected BLM localized at discrete foci around viral replication centers. These studies identify BLM as a new substrate for degradation by the adenovirus E1b55K/E4orf6 complex.
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Drosophila RecQ5 is required for efficient SSA repair and suppression of LOH in vivo. Protein Cell 2010; 1:478-90. [PMID: 21203963 DOI: 10.1007/s13238-010-0058-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2010] [Accepted: 04/25/2010] [Indexed: 10/19/2022] Open
Abstract
RecQ5 in mammalian cells has been suggested to suppress inappropriate homologous recombination. However, the specific pathway(s) in which it is involved and the underlining mechanism(s) remain poorly understood. We took advantage of genetic tools in Drosophila to investigate how Drosophila RecQ5 (dRecQ5) functions in vivo in homologous recombination-mediated double strand break (DSB) repair. We generated null alleles of dRecQ5 using the targeted recombination technique. The mutant animals are homozygous viable, but with growth retardation during development. The mutants are sensitive to both exogenous DSB-inducing treatment, such as gamma-irradiation, and endogenously induced double strand breaks (DSBs) by I-Sce I endonuclease. In the absence of dRecQ5, single strand annealing (SSA)-mediated DSB repair is compromised with compensatory increases in either inter-homologous gene conversion, or non-homologous end joining (NHEJ) when inter-chromosomal homologous sequence is unavailable. Loss of function of dRecQ5 also leads to genome instability in loss of heterozygosity (LOH) assays. Together, our data demonstrate that dRecQ5 functions in SSA-mediated DSB repair to achieve its full efficiency and in suppression of LOH in Drosophila.
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Robertson HM. The choanoflagellate Monosiga brevicollis karyotype revealed by the genome sequence: telomere-linked helicase genes resemble those of some fungi. Chromosome Res 2009; 17:873-82. [PMID: 19789987 DOI: 10.1007/s10577-009-9078-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2009] [Revised: 08/06/2009] [Accepted: 08/13/2009] [Indexed: 12/01/2022]
Abstract
The approximately 42 Mbp assembled genome sequence for the choanoflagellate Monosiga brevicollis reveals that most of the large scaffolds of 300-2,600 kb represent entire chromosomes or chromosome arms. Telomeres are partially assembled at the termini of 37 scaffolds, while another 43 scaffolds end in telomere-associated regions containing distinctive gene sets. Potential centromeric regions were identified on 39 scaffolds. Together, these observations suggest a karyotype of approximately 40 metacentric and submetacentric chromosomes averaging 1 Mbp in size. Genes encoding RecQ family DNA helicases, along with ankyrin-domain proteins and serine/threonine kinases, are associated with most telomeres, a feature shared with some fungi. This telomere-linked helicase gene arrangement might be ancestral to both fungi and choanoflagellates in the super-kingdom Opisthokonta; however, the great lability of telomere architecture suggests that it could also be a convergent feature.
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Affiliation(s)
- Hugh M Robertson
- Department of Entomology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA.
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20
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Xu Y, Lei Z, Huang H, Dui W, Liang X, Ma J, Jiao R. dRecQ4 is required for DNA synthesis and essential for cell proliferation in Drosophila. PLoS One 2009; 4:e6107. [PMID: 19572017 PMCID: PMC2700968 DOI: 10.1371/journal.pone.0006107] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2009] [Accepted: 06/02/2009] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND The family of RecQ DNA helicases plays an important role in the maintenance of genomic integrity. Mutations in three of the five known RecQ family members in humans, BLM, WRN and RecQ4, lead to disorders that are characterized by predisposition to cancer and premature aging. METHODOLOGY/PRINCIPAL FINDINGS To address the in vivo functions of Drosophila RecQ4 (dRecQ4), we generated mutant alleles of dRecQ4 using the targeted gene knock-out technique. Our data show that dRecQ4 mutants are homozygous lethal with defects in DNA replication, cell cycle progression and cell proliferation. Two sets of experiments suggest that dRecQ4 also plays a role in DNA double strand break repair. First, mutant animals exhibit sensitivity to gamma irradiation. Second, the efficiency of DsRed reconstitution via single strand annealing repair is significantly reduced in the dRecQ4 mutant animals. Rescue experiments further show that both the N-terminal domain and the helicase domain are essential to dRecQ4 function in vivo. The N-terminal domain is sufficient for the DNA repair function of dRecQ4. CONCLUSIONS/SIGNIFICANCE Together, our results show that dRecQ4 is an essential gene that plays an important role in not only DNA replication but also DNA repair and cell cycle progression in vivo.
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Affiliation(s)
- Yanjuan Xu
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, the Chinese Academy of Sciences, Beijing, China
- Graduate School of the Chinese Academy of Sciences, Beijing, China
| | - Zhiyong Lei
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, the Chinese Academy of Sciences, Beijing, China
| | - Hai Huang
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, the Chinese Academy of Sciences, Beijing, China
- Graduate School of the Chinese Academy of Sciences, Beijing, China
| | - Wen Dui
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, the Chinese Academy of Sciences, Beijing, China
- Graduate School of the Chinese Academy of Sciences, Beijing, China
| | - Xuehong Liang
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, the Chinese Academy of Sciences, Beijing, China
| | - Jun Ma
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, the Chinese Academy of Sciences, Beijing, China
- Divisions of Biomedical Informatics and Developmental Biology, Cincinnati Children's Hospital Research Foundation, Cincinnati, Ohio, United States of America
| | - Renjie Jiao
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, the Chinese Academy of Sciences, Beijing, China
- * E-mail:
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Piontkivska H, Yang MQ, Larkin DM, Lewin HA, Reecy J, Elnitski L. Cross-species mapping of bidirectional promoters enables prediction of unannotated 5' UTRs and identification of species-specific transcripts. BMC Genomics 2009; 10:189. [PMID: 19393065 PMCID: PMC2688522 DOI: 10.1186/1471-2164-10-189] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2008] [Accepted: 04/24/2009] [Indexed: 11/10/2022] Open
Abstract
Background Bidirectional promoters are shared regulatory regions that influence the expression of two oppositely oriented genes. This type of regulatory architecture is found more frequently than expected by chance in the human genome, yet many specifics underlying the regulatory design are unknown. Given that the function of most orthologous genes is similar across species, we hypothesized that the architecture and regulation of bidirectional promoters might also be similar across species, representing a core regulatory structure and enabling annotation of these regions in additional mammalian genomes. Results By mapping the intergenic distances of genes in human, chimpanzee, bovine, murine, and rat, we show an enrichment for pairs of genes equal to or less than 1,000 bp between their adjacent 5' ends ("head-to-head") compared to pairs of genes that fall in the same orientation ("head-to-tail") or whose 3' ends are side-by-side ("tail-to-tail"). A representative set of 1,369 human bidirectional promoters was mapped to orthologous sequences in other mammals. We confirmed predictions for 5' UTRs in nine of ten manual picks in bovine based on comparison to the orthologous human promoter set and in six of seven predictions in human based on comparison to the bovine dataset. The two predictions that did not have orthology as bidirectional promoters in the other species resulted from unique events that initiated transcription in the opposite direction in only those species. We found evidence supporting the independent emergence of bidirectional promoters from the family of five RecQ helicase genes, which gained their bidirectional promoters and partner genes independently rather than through a duplication process. Furthermore, by expanding our comparisons from pairwise to multispecies analyses we developed a map representing a core set of bidirectional promoters in mammals. Conclusion We show that the orthologous positions of bidirectional promoters provide a reliable guide to directly annotate over one thousand regulatory regions in sequences of mammalian genomes, while also serving as a useful tool to predict 5' UTR positions and identify genes that are novel to a single species.
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Affiliation(s)
- Helen Piontkivska
- 2Department of BiologicalSciences, Kent State University, Kent, Ohio 44242, USA.
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22
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Kappeler M, Kranz E, Woolcock K, Georgiev O, Schaffner W. Drosophila bloom helicase maintains genome integrity by inhibiting recombination between divergent DNA sequences. Nucleic Acids Res 2008; 36:6907-17. [PMID: 18978019 PMCID: PMC2588521 DOI: 10.1093/nar/gkn793] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
DNA double strand breaks (DSB) can be repaired either via a sequence independent joining of DNA ends or via homologous recombination. We established a detection system in Drosophila melanogaster to investigate the impact of sequence constraints on the usage of the homology based DSB repair via single strand annealing (SSA), which leads to recombination between direct repeats with concomitant loss of one repeat copy. First of all, we find the SSA frequency to be inversely proportional to the spacer length between the repeats, for spacers up to 2.4 kb in length. We further show that SSA between divergent repeats (homeologous SSA) is suppressed in cell cultures and in vivo in a sensitive manner, recognizing sequence divergences smaller than 0.5%. Finally, we demonstrate that the suppression of homeologous SSA depends on the Bloom helicase (Blm), encoded by the Drosophila gene mus309. Suppression of homeologous recombination is a novel function of Blm in ensuring genomic integrity, not described to date in mammalian systems. Unexpectedly, distinct from its function in Saccharomyces cerevisiae, the mismatch repair factor Msh2 encoded by spel1 does not suppress homeologous SSA in Drosophila.
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Affiliation(s)
- Michael Kappeler
- Insitut für Molekularbiologie der Universität Zürich, Zürich, Switzerland
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23
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Hyun M, Bohr VA, Ahn B. Biochemical characterization of the WRN-1 RecQ helicase of Caenorhabditis elegans. Biochemistry 2008; 47:7583-93. [PMID: 18558712 DOI: 10.1021/bi800197m] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The highly conserved RecQ helicases are essential for the maintenance of genomic stability. Werner syndrome protein, WRN, is one of five human RecQ helicase homologues, and a deficiency of the protein causes a hereditary premature aging disorder that is characterized by genomic instability. A WRN orthologue, wrn-1 lacking the exonuclease domain, has been identified in the nematode Caenorhabditis elegans. wrn-1(RNAi) in C. elegans has a shortened life span, increased sensitivity to DNA damage, and accelerated aging phenotypes. However, little is known about its enzymatic activity. We purified the recombinant C. elegans WRN-1 protein (CeWRN-1) and then investigated its substrate specificity in vitro to improve our understanding of its function in vivo. We found that CeWRN-1 is an ATP-dependent 3'-5' helicase capable of unwinding a variety of DNA structures such as forked duplexes, Holliday junctions, bubble substrates, D-loops, and flap duplexes, and 3'-tailed duplex substrates. Distinctly, CeWRN-1 is able to unwind a long forked duplex compared to human WRN. Furthermore, CeWRN-1 helicase activity on a long DNA duplex is stimulated by C. elegans replication protein A (CeRPA) that is shown to interact with CeWRN-1 by a dot blot. The ability of CeWRN-1 to unwind these DNA structures may improve the access for DNA repair and replication proteins that are important for preventing the accumulation of abnormal structures, contributing to genomic stability.
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Affiliation(s)
- Moonjung Hyun
- Department of Life Sciences, University of Ulsan, Ulsan 680749, Korea
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Trowbridge K, McKim K, Brill SJ, Sekelsky J. Synthetic lethality of Drosophila in the absence of the MUS81 endonuclease and the DmBlm helicase is associated with elevated apoptosis. Genetics 2007; 176:1993-2001. [PMID: 17603121 PMCID: PMC1950608 DOI: 10.1534/genetics.106.070060] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Mus81-Mms4 (Mus81-Eme1 in some species) is a heterodimeric DNA structure-specific endonuclease that has been implicated in meiotic recombination and processing of damaged replication forks in fungi. We generated and characterized mutations in Drosophila melanogaster mus81 and mms4. Unlike the case in fungi, we did not find any role for MUS81-MMS4 in meiotic crossing over. A possible role for this endonuclease in repairing double-strand breaks that arise during DNA replication is suggested by the finding that mus81 and mms4 mutants are hypersensitive to camptothecin; however, these mutants are not hypersensitive to other agents that generate lesions that slow or block DNA replication. In fungi, mus81, mms4, and eme1 mutations are synthetically lethal with mutations in genes encoding RecQ helicase homologs. Similarly, we found that mutations in Drosophila mus81 and mms4 are synthetically lethal with null mutations in mus309, which encodes the ortholog of the Bloom Syndrome helicase. Synthetic lethality is associated with high levels of apoptosis in proliferating tissues. Lethality and elevated apoptosis were partially suppressed by a mutation in spn-A, which encodes the ortholog of the strand invasion protein Rad51. These findings provide insights into the causes of synthetic lethality.
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Affiliation(s)
- Kirsten Trowbridge
- Curriculum in Genetics and Molecular Biology, University of North Carolina, Chapel Hill, NC 27599, USA
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25
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Weinert BT, Rio DC. DNA strand displacement, strand annealing and strand swapping by the Drosophila Bloom's syndrome helicase. Nucleic Acids Res 2007; 35:1367-76. [PMID: 17272294 PMCID: PMC1849897 DOI: 10.1093/nar/gkl831] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Genetic analysis of the Drosophila Bloom's syndrome helicase homolog (mus309/DmBLM) indicates that DmBLM is required for the synthesis-dependent strand annealing (SDSA) pathway of homologous recombination. Here we report the first biochemical study of DmBLM. Recombinant, epitope-tagged DmBLM was expressed in Drosophila cell culture and highly purified protein was prepared from nuclear extracts. Purified DmBLM exists exclusively as a high molecular weight (∼1.17 MDa) species, is a DNA-dependent ATPase, has 3′→5′ DNA helicase activity, prefers forked substrate DNAs and anneals complementary DNAs. High-affinity DNA binding is ATP-dependent and low-affinity ATP-independent interactions contribute to forked substrate DNA binding and drive strand annealing. DmBLM combines DNA strand displacement with DNA strand annealing to catalyze the displacement of one DNA strand while annealing a second complementary DNA strand.
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Affiliation(s)
| | - Donald C. Rio
- To whom correspondence should be addressed. Tel: +1 510 642 1071; Fax: +1 510 642 6062;
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26
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Johnson-Schlitz D, Engels WR. Template disruptions and failure of double Holliday junction dissolution during double-strand break repair in Drosophila BLM mutants. Proc Natl Acad Sci U S A 2006; 103:16840-5. [PMID: 17075047 PMCID: PMC1636541 DOI: 10.1073/pnas.0607904103] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Previous biochemical studies of the BLM gene product have shown its ability in conjunction with topoisomerase IIIalpha to resolve double Holliday structures through a process called "dissolution." This process could prevent crossing over during repair of double-strand breaks. We report an analysis of the Drosophila BLM gene, DmBlm, in the repair of double-strand breaks in the premeiotic germ line of Drosophila males. With a repair reporter construct, Rr3, and other genetic tools, we show that DmBlm mutants are defective for homologous repair but show a compensating increase in single-strand annealing. Increases of 40- to 50-fold in crossing over and flanking deletions also were seen. Perhaps most significantly, the template used for homologous repair in DmBlm mutants is itself subject to deletions and complex rearrangements. These template disruptions are indicative of failure to resolve double Holliday junctions. These findings, along with the demonstration that a weak allele of topoisomerase IIIalpha has some of the same defects as DmBlm, support the dissolution model. Finally, an analysis of DmBlm mutants in conjunction with mus81 or spnA (Rad51) reveals a second function of BLM distinct from the repair of induced double-strand breaks and possibly related to maintenance of replication forks.
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Affiliation(s)
| | - William R. Engels
- Genetics Department, University of Wisconsin, Madison, WI 53706
- To whom correspondence should be addressed. E-mail:
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27
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Lankenau DH. Germline Double-Strand Break Repair and Gene Targeting in Drosophila: A Trajectory System throughout Evolution. Genome Integr 2006. [DOI: 10.1007/7050_019] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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28
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Saotome A, Kimura S, Mori Y, Uchiyama Y, Morohashi K, Sakaguchi K. Characterization of four RecQ homologues from rice (Oryza sativa L. cv. Nipponbare). Biochem Biophys Res Commun 2006; 345:1283-91. [PMID: 16730655 DOI: 10.1016/j.bbrc.2006.04.134] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2006] [Accepted: 04/14/2006] [Indexed: 11/19/2022]
Abstract
The RecQ family of DNA helicases is conserved throughout the biological kingdoms. In this report, we have characterized four RecQ homologues clearly expressed in rice. OsRecQ1, OsRecQ886, and OsRecQsim expressions were strongly detected in meristematic tissues. Transcription of the OsRecQ homologues was differentially induced by several types of DNA-damaging agents. The expression of four OsRecQ homologues was induced by MMS and bleomycin. OsRecQ1 and OsRecQ886 were induced by H(2)O(2), and MitomycinC strongly induced the expression of OsRecQ1. Transient expression of OsRecQ/GFP fusion proteins demonstrated that OsRecQ2 and OsRecQ886 are found in nuclei, whereas OsRecQ1 and OsRecQsim are found in plastids. Neither OsRecQ1 nor OsRecQsim are induced by light. These results indicate that four of the RecQ homologues have different and specific functions in DNA repair pathways, and that OsRecQ1 and OsRecQsim may not involve in plastid differentiation but different aspects of a plastid-specific DNA repair system.
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Affiliation(s)
- Ai Saotome
- Department of Applied Biological Science, Faculty of Science and Technology, Tokyo University of Science, Noda-shi, Chiba-ken, Japan
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29
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Zaritsky A, Woldringh CL, Einav M, Alexeeva S. Use of thymine limitation and thymine starvation to study bacterial physiology and cytology. J Bacteriol 2006; 188:1667-79. [PMID: 16484178 PMCID: PMC1426543 DOI: 10.1128/jb.188.5.1667-1679.2006] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Affiliation(s)
- Arieh Zaritsky
- Department of Life Sciences, Ben-Gurion University of the Negev, POB 653, Be'er-Sheva 84105, Israel.
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30
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Zhang XD, Dou SX, Xie P, Wang PY, Xi XG. RecQ helicase-catalyzed DNA unwinding detected by fluorescence resonance energy transfer. Acta Biochim Biophys Sin (Shanghai) 2005; 37:593-600. [PMID: 16143813 DOI: 10.1111/j.1745-7270.2005.00084.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
A fluorometric assay was used to study the DNA unwinding kinetics induced by Escherichia coli RecQ helicase. This assay was based on fluorescence resonance energy transfer and carried out on stopped-flow, in which DNA unwinding was monitored by fluorescence emission enhancement of fluorescein resulting from helicase-catalyzed DNA unwinding. By this method, we determined the DNA unwinding rate of RecQ at different enzyme concentrations. We also studied the dependences of DNA unwinding magnitude and rate on magnesium ion concentration. We showed that this method could be used to determine the polarity of DNA unwinding. This assay should greatly facilitate further study of the mechanism for RecQ-catalyzed DNA unwinding.
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Affiliation(s)
- Xing-Dong Zhang
- Laboratory of Soft Matter Physics, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China
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31
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Spresser CR, Carlson KA. Drosophila melanogaster as a complementary system for studying HIV-1-related genes and proteins. J Neurosci Res 2005; 80:451-5. [PMID: 15795932 DOI: 10.1002/jnr.20460] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Human immunodeficiency virus type 1 (HIV-1) persists as a pandemic even though new information about the virus is being discovered on a daily basis. If the brain becomes infected, HIV-1 encephalitis or HIV-1-associated dementia may develop. There is much to be learned about the modes of action and mechanisms of genes and proteins, and their interactions that underlie HIV-1 infection. Drosophila melanogaster has been used successfully to study genes and proteins related to HIV-1 infection, including but not limited to the disturbance of antimicrobial responses by viral protein U and the identification of D. melanogaster analogs to the serine palmitoyltransferase 5 and 6 proteins that play a role in activation of transcription by the HIV-1 Tat protein in human cells. We believe that utilizing D. melanogaster as a complementary system for the study of genes and proteins related to HIV-1 infection will provide useful information that will lead to new studies designed to enhance our understanding of the mechanistic roles of these molecules. In the present study, we focus on the utilization of D. melanogaster as a complementary system for studying HIV-1 related genes and proteins, why this research should be extended, and why this complementary system is an important method for enhancing our understanding of the genetics involved in HIV-1 infection.
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Affiliation(s)
- Cole R Spresser
- Biology Department, University of Nebraska at Kearney, Kearney, Nebraska 68849, USA
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32
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Onoda F, Seki M, Wang W, Enomoto T. The hyper unequal sister chromatid recombination in an sgs1 mutant of budding yeast requires MSH2. DNA Repair (Amst) 2005; 3:1355-62. [PMID: 15336630 DOI: 10.1016/j.dnarep.2004.05.008] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/07/2004] [Indexed: 11/22/2022]
Abstract
Budding yeast SGS1 and the human Bloom's syndrome (BS) gene, BLM, are homologues of the Escherichia coli recQ. Cells derived from BS patients are characterized by a dramatic increase in sister chromatid exchange (SCE). We previously reported that budding yeast cells deficient in SGS1 showed an increase in the frequency of recombination between unequal sister chromatids recombination (USCR). In this study, we examined the factors influencing the elevated SCR frequency in sgs1 disruptants. The increase in SCR frequency in sgs1 mutants was greatly reduced by disrupting the RAD52 or MSH2 gene, which is involved in mismatch repair. However, a plasmid carrying MSH2, having a missense mutation defective in mismatch repair complemented the reduced USCR in msh2 sgs1 mutants, suggesting that the function of Msh2 in mismatch repair is dispensable for USCR.
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Affiliation(s)
- Fumitoshi Onoda
- Molecular Cell Biology Laboratory, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba Aramaki, Aoba-ku, Sendai 980-8578, Japan
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33
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Yamana Y, Maeda T, Ohba H, Usui T, Ogawa HI, Kusano K. Regulation of homologous integration in yeast by the DNA repair proteins Ku70 and RecQ. Mol Genet Genomics 2005; 273:167-76. [PMID: 15803320 DOI: 10.1007/s00438-005-1108-y] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2004] [Accepted: 01/06/2005] [Indexed: 11/25/2022]
Abstract
The product of the BLM gene, which is mutated in Bloom syndrome in humans, and the Saccharomyces cerevisiae protein Sgs1 are both homologous to the Escherichia coli DNA helicase RecQ, and have been shown to be involved in the regulation of homologous recombination. Mutations in these genes result in genome instability because they increase the incidence of deletions and translocations. We present evidence for a genetic interaction between SGS1 and YKU70, which encodes the S. cerevisiae homologue of the human DNA helicase Ku70. In a yku70 mutant background, sgs1 mutations increased sensitivity to DNA breakage induced either by treatment with camptothecin or by the expression of the restriction enzyme EcoRI. The yku70 mutation caused a fourfold increase in the rate of double-strand break (DSB)-induced target integration as that seen in the sgs1 mutant. The combination of yku70 and sgs1 mutations additively increased the rate of the targeted integration, and this effect was completely suppressed by deletion of RAD51. Interestingly, an extra copy of YKU70 partially suppressed the increase in targeted integration seen in the sgs1 single mutant. These results suggest that Yku70 modulates the repair of DSBs associated with homologous recombination in a different way from Sgs1, and that the inactivation of RecQ and Ku70 homologues may enhance the frequency of gene targeting in higher eukaryotes.
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Affiliation(s)
- Yoshimasa Yamana
- Department of Biological Functions and Engineering, Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, 2-4 Hibikino, Wakamatsu-ku, Kitakyushu, 808-0196, Japan
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Nakayama M, Kawasaki K, Matsumoto K, Shibata T. The possible roles of the DNA helicase and C-terminal domains in RECQ5/QE: complementation study in yeast. DNA Repair (Amst) 2004; 3:369-78. [PMID: 15010312 DOI: 10.1016/j.dnarep.2003.12.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/02/2003] [Indexed: 11/26/2022]
Abstract
DmRECQ5/QE is a member of the RECQ5 subfamily, which shares homology with the Escherichia coli RecQ DNA helicase. Although the DNA helicase activity of RECQ5/QE has been characterized in vitro, the in vivo function of RECQ5/QE was essentially unknown. To investigate the cellular role of RECQ5, the potential of RECQ5/QE was evaluated by substitution of the only RecQ-like helicase, Sgs1, in budding yeast. RECQ5/QE can complement several phenotypes of sgs1, including the synthetic growth defect with srs2, the hypersensitivity to hydroxyurea and methyl methanesulfonate, and the elevated frequency of homologous recombination and sister chromatid exchange (SCE), but poorly complemented the suppression of slow growth in top3. These data suggested that RECQ5/QE exhibits an evolutionarily conserved RecQ function in vivo. The RECQ5/QE domain necessary for the yeast complementation was determined. The helicase domain and helicase activity were required to complement both the sgs1srs2 and sgs1top3 phenotypes. In contrast, the C-terminal domain was dispensable for complementing the sgs1srs2 phenotype, but was required for the sgs1top3 phenotype. These results suggested that the RECQ5/QE helicase activity is important for cellular function and that the C-terminal domain has a specific function in the absence of Top3.
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Affiliation(s)
- Minoru Nakayama
- Cellular and Molecular Biology Laboratory, RIKEN (The Institute of Physical and Chemical Research), Hirosawa, Wako-shi, Saitama, Japan
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35
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Schmidt KH, Kolodner RD. Requirement of Rrm3 helicase for repair of spontaneous DNA lesions in cells lacking Srs2 or Sgs1 helicase. Mol Cell Biol 2004; 24:3213-26. [PMID: 15060145 PMCID: PMC381612 DOI: 10.1128/mcb.24.8.3213-3226.2004] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Rrm3 DNA helicase of Saccharomyces cerevisiae interacts with proliferating cell nuclear antigen and is required for replication fork progression through ribosomal DNA repeats and subtelomeric and telomeric DNA. Here, we show that rrm3 srs2 and rrm3 sgs1 mutants, in which two different DNA helicases have been inactivated, exhibit a severe growth defect and undergo frequent cell death. Cells lacking Rrm3 and Srs2 arrest in the G(2)/M phase of the cell cycle with 2N DNA content and frequently contain only a single nucleus. The phenotypes of rrm3 srs2 and rrm3 sgs1 mutants were suppressed by disrupting early steps of homologous recombination. These observations identify Rrm3 as a new member of a network of pathways, involving Sgs1 and Srs2 helicases and Mus81 endonuclease, suggested to act during repair of stalled replication forks.
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Affiliation(s)
- Kristina H Schmidt
- Ludwig Institute for Cancer Research, University of California-San Diego School of Medicine, La Jolla, California 92093, USA
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36
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Harmon FG, Brockman JP, Kowalczykowski SC. RecQ helicase stimulates both DNA catenation and changes in DNA topology by topoisomerase III. J Biol Chem 2003; 278:42668-78. [PMID: 12909639 DOI: 10.1074/jbc.m302994200] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Together, RecQ helicase and topoisomerase III (Topo III) of Escherichia coli comprise a potent DNA strand passage activity that can catenate covalently closed DNA (Harmon, F. G., DiGate, R. J., and Kowalczykowski, S. C. (1999) Mol. Cell 3, 611-620). Here we directly assessed the structure of the catenated DNA species formed by RecQ helicase and Topo III using atomic force microscopy. The images show complex catenated DNA species involving crossovers between multiple double-stranded DNA molecules that are consistent with full catenanes. E. coli single-stranded DNA-binding protein significantly stimulated both the topoisomerase activity of Topo III alone and the DNA strand passage activity of RecQ helicase and Topo III. Titration data suggest that an intermediate of the RecQ helicase unwinding process, perhaps a RecQ helicase-DNA fork, is the target for Topo III action. Catenated DNA is the predominant product under conditions of molecular crowding; however, we also discovered that RecQ helicase and single-stranded DNA-binding protein greatly stimulated the intramolecular strand passage ("supercoiling") activity of Topo III, as revealed by changes in the linking number of uncatenated DNA. Together our results demonstrate that RecQ helicase and Topo III function together to comprise a potent and concerted single-strand DNA passage activity that can mediate both catenation-decatenation processes and changes in DNA topology.
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Affiliation(s)
- Frank G Harmon
- Division of Biological Sciences, Section of Microbiology, Center for Genetics and Development, University of California-Davis, 1 Shields Avenue, Davis, CA 95616, USA
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37
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Bagherieh-Najjar MB, de Vries OMH, Kroon JTM, Wright EL, Elborough KM, Hille J, Dijkwel PP. Arabidopsis RecQsim, a plant-specific member of the RecQ helicase family, can suppress the MMS hypersensitivity of the yeast sgs1 mutant. PLANT MOLECULAR BIOLOGY 2003; 52:273-284. [PMID: 12856935 DOI: 10.1023/a:1023968429220] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The Arabidopsis genome contains seven genes that belong to the RecQ family of ATP-dependent DNA helicases. RecQ members in Saccharomyces cerevisiae (SGS1) and man (WRN, BLM and RecQL4) are involved in DNA recombination, repair and genome stability maintenance, but little is known about the function of their plant counterparts. The Arabidopsis thaliana RecQsim gene is remarkably different from the other RecQ-like genes due to an insertion in its helicase domain. We isolated the AtRecQsim orthologues from rice and rape and established the presence of a similar insertion in their helicase domain, which suggests a plant specific function for the insert. The expression pattern of the AtRecQsim gene was compared with the other Arabidopsis RecQ-like members in different tissues and in response to stress. The transcripts of the AtRecQsim gene were found in all plant organs and its accumulation was higher in roots and seedlings, as compared to the other AtRecQ-like members. In contrast to most AtRecQ-like genes, the examined environmental cues did not have a detectable effect on the accumulation of the AtRecQsim transcripts. The budding yeast sgs1 mutant, which is known to be hypersensitive to the DNA-damaging drug MMS, was transformed with the AtRecQsim cDNA. The AtRecQsim gene suppressed the MMS hypersensitivity phenotype of the sgs1 cells. We propose that the Arabidopsis RecQsim gene, despite its unusual structure, exhibits an evolutionary conserved function.
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Affiliation(s)
- Mohammad B Bagherieh-Najjar
- Molecular Biology of Plants, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands
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38
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Wang W, Seki M, Narita Y, Nakagawa T, Yoshimura A, Otsuki M, Kawabe YI, Tada S, Yagi H, Ishii Y, Enomoto T. Functional relation among RecQ family helicases RecQL1, RecQL5, and BLM in cell growth and sister chromatid exchange formation. Mol Cell Biol 2003; 23:3527-35. [PMID: 12724411 PMCID: PMC164753 DOI: 10.1128/mcb.23.10.3527-3535.2003] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Human RECQL1 and RECQL5 belong to the RecQ family that includes Bloom syndrome, Werner syndrome, and Rothmund-Thomson syndrome causative genes. Cells derived from individuals suffering from these syndromes show significant levels of genomic instability. However, neither RECQL1 nor RECQL5 has been related to a disease, and nothing is known about the functions of RecQL1 and RecQL5. We generated here RECQL1(-/-), RECQL5(-/-), RECQL1(-/-)/RECQL5(-/-), RECQL1(-/-)/BLM(-/-), and RECQL5(-/-)/BLM(-/-) cells from chicken B-lymphocyte line DT40 cells. Although BLM(-/-) DT40 cells showed a slow-growth phenotype, a higher sensitivity to methyl methanesulfonate than the wild type, and an approximately 10-fold increase in the frequency of sister chromatid exchange (SCE) compared to wild-type cells, RECQL1(-/-), RECQL5(-/-), and RECQL1(-/-)/RECQL5(-/-) cells showed no significant difference from the wild-type cells in growth, sensitivity to DNA-damaging agents, and the frequency of SCE. However, both RECQL1(-/-)/BLM(-/-) and RECQL5(-/-)/BLM(-/-) cells grew more slowly than BLM(-/-) cells because of the increase in the population of dead cells, indicating that RecQL1 and RecQL5 are somehow involved in cell viability under the BLM function-impaired condition. Surprisingly, RECQL5(-/-)/BLM(-/-) cells showed a higher frequency of SCE than BLM(-/-) cells, indicating that RecQL5 suppresses SCE under the BLM function-impaired condition.
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Affiliation(s)
- Wensheng Wang
- Molecular Cell Biology Laboratory, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba, Aramaki, Aoba-ku, Sendai 980-8578, Japan
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39
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Cui S, Klima R, Ochem A, Arosio D, Falaschi A, Vindigni A. Characterization of the DNA-unwinding activity of human RECQ1, a helicase specifically stimulated by human replication protein A. J Biol Chem 2003; 278:1424-32. [PMID: 12419808 DOI: 10.1074/jbc.m209407200] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The RecQ helicases are involved in several aspects of DNA metabolism. Five members of the RecQ family have been found in humans, but only two of them have been carefully characterized, BLM and WRN. In this work, we describe the enzymatic characterization of RECQ1. The helicase has 3' to 5' polarity, cannot start the unwinding from a blunt-ended terminus, and needs a 3'-single-stranded DNA tail longer than 10 nucleotides to open the substrate. However, it was also able to unwind a blunt-ended duplex DNA with a "bubble" of 25 nucleotides in the middle, as previously observed for WRN and BLM. We show that only short DNA duplexes (<30 bp) can be unwound by RECQ1 alone, but the addition of human replication protein A (hRPA) increases the processivity of the enzyme (>100 bp). Our studies done with Escherichia coli single-strand binding protein (SSB) indicate that the helicase activity of RECQ1 is specifically stimulated by hRPA. This finding suggests that RECQ1 and hRPA may interact also in vivo and function together in DNA metabolism. Comparison of the present results with previous studies on WRN and BLM provides novel insight into the role of the N- and C-terminal domains of these helicases in determining their substrate specificity and in their interaction with hRPA.
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Affiliation(s)
- Sheng Cui
- International Centre for Genetic Engineering and Biotechnology, Padriciano 99, I-34012 Trieste, Italy
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40
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Pickford A, Braccini L, Macino G, Cogoni C. The QDE-3 homologue RecQ-2 co-operates with QDE-3 in DNA repair in Neurospora crassa. Curr Genet 2003; 42:220-7. [PMID: 12589473 DOI: 10.1007/s00294-002-0351-6] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2002] [Revised: 09/15/2002] [Accepted: 09/28/2002] [Indexed: 12/26/2022]
Abstract
The post-transcriptional gene silencing mechanism in Neurospora crassa, called quelling, was shown to involve the products of three genes termed quelling-defective. A homologue to the qde-3 gene encoding a putative RecQ-type DNA helicase was isolated and was named RecQ-2. Characterisation of the RecQ-2 gene has revealed that it is not involved in quelling, but may co-operate with the qde-3 gene product in a pathway that repairs damage to DNA caused by the chemical mutagens methyl methanesulfonate and N-methyl- N'-nitro- N-nitrosoguanidine. These results indicate that the qde-3 RecQ helicase may have a dual role in N. crassa, either acting alone as an essential component of the quelling mechanism or together with the RecQ-2 RecQ helicase, as part of a process to repair DNA lesions during replication.
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Affiliation(s)
- A Pickford
- Istituto Pasteur, Fondazione Cenci Bolognetti, Dipartimento di Biotecnologie Cellulari e Ematologia, Università degli Studi La Sapienza, Viale Regina Elena 324, 00161 Rome, Italy
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41
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Ahmad F, Kaplan CD, Stewart E. Helicase activity is only partially required for Schizosaccharomyces pombe Rqh1p function. Yeast 2002; 19:1381-98. [PMID: 12478586 DOI: 10.1002/yea.917] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The RecQ-related family of DNA helicases is required for the maintenance of genomic stability in organisms ranging from bacteria to humans. In humans, mutation of three RecQ-related helicases, BLM, WRN and RecQL4, cause the cancer-prone and premature ageing diseases of Bloom syndrome, Werner's syndrome and Rothmund-Thompson syndrome, respectively. In the fission yeast Schizosaccharomyces pombe, disruption of the rqh1(+) gene, which encodes the single Sz. pombe RecQ-related helicase, causes cells to display reduced viability and elevated levels of chromosome loss. After S-phase arrest or DNA damage, cells lacking rqh1(+) function display elevated levels of homologous recombination and defective chromosome segregation. Here we show that, like other RecQ family members, the Rqh1p protein displays 3' to 5' DNA helicase activity. Interestingly, however, unlike other RecQ family members, the helicase activity of Rqh1p is only partially required for its function in recovery from S-phase arrest or DNA damage. We also report that high cellular levels of Rqh1p result in lethal chromosome segregation defects, while more moderate levels of Rqh1p cause significantly elevated rates of chromosome loss. This suggests that careful regulation of RecQ-like protein levels in eukaryotic cells is vital for maintaining genome stability.
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Affiliation(s)
- Fouzia Ahmad
- School of Biological Sciences, University of Manchester, Manchester, UK
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42
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Kaliraman V, Brill SJ. Role of SGS1 and SLX4 in maintaining rDNA structure in Saccharomyces cerevisiae. Curr Genet 2002; 41:389-400. [PMID: 12228808 PMCID: PMC2804045 DOI: 10.1007/s00294-002-0319-6] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2002] [Revised: 06/25/2002] [Accepted: 06/25/2002] [Indexed: 12/12/2022]
Abstract
To address the role of SGS1 in controlling genome stability we previously identified several slx mutants that require SGS1 for viability. Here, we report the isolation and characterization of temperature-sensitive (ts) SGS1 alleles in cells lacking SLX4. At the non-permissive temperature (37 degrees C) sgs1-ts slx4 cells progress through S-phase and arrest growth as large-budded cells with at least a 2C DNA content. Analysis of the integrity of the replicated DNA by pulsed-field gel electrophoresis revealed that chromosome XII (ChrXII) was uniquely altered, as it was unable to enter the gel. This defect was specific to the tandem rDNA repeats on ChrXII and occurred as cells progressed through S-phase at 37 degrees C. Reciprocal-shift experiments revealed that viability and ChrXII migration can be restored by allowing Sgs1 to act between G2/M and the subsequent G1 phase. These results suggest that Sgs1 and Slx4 are not required for bulk DNA synthesis but play redundant roles in maintaining rDNA structure during DNA replication.
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Affiliation(s)
| | - Steven J. Brill
- Department of Molecular Biology and Biochemistry, 679 Hoes Lane, CABM, Rutgers University, Piscataway, NJ 08854
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van Brabant AJ, Stan R, Ellis NA. DNA helicases, genomic instability, and human genetic disease. Annu Rev Genomics Hum Genet 2002; 1:409-59. [PMID: 11701636 DOI: 10.1146/annurev.genom.1.1.409] [Citation(s) in RCA: 167] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
DNA helicases are a highly conserved group of enzymes that unwind DNA. They function in all processes in which access to single-stranded DNA is required, including DNA replication, DNA repair and recombination, and transcription of RNA. Defects in helicases functioning in one or more of these processes can result in characteristic human genetic disorders in which genomic instability and predisposition to cancer are common features. So far, different helicase genes have been found mutated in six such disorders. Mutations in XPB and XPD can result in xeroderma pigmentosum, Cockayne syndrome, or trichothiodystrophy. Mutations in the RecQ-like genes BLM, WRN, and RECQL4 can result in Bloom syndrome, Werner syndrome, and Rothmund-Thomson syndrome, respectively. Because XPB and XPD function in both nucleotide excision repair and transcription initiation, the cellular phenotypes associated with a deficiency of each one of them include failure to repair mutagenic DNA lesions and defects in the recovery of RNA transcription after UV irradiation. The functions of the RecQ-like genes are unknown; however, a growing body of evidence points to a function in restarting DNA replication after the replication fork has become stalled. The genomic instability associated with mutations in the RecQ-like genes includes spontaneous chromosome instability and elevated mutation rates. Mouse models for nearly all of these entities have been developed, and these should help explain the widely different clinical features that are associated with helicase mutations.
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Affiliation(s)
- A J van Brabant
- Department of Human Genetics, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA
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44
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Ohhata T, Araki R, Fukumura R, Kuroiwa A, Matsuda Y, Abe M. Cloning, genomic structure and chromosomal localization of the gene encoding mouse DNA helicase RECQL5beta. Gene 2001; 280:59-66. [PMID: 11738818 DOI: 10.1016/s0378-1119(01)00740-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Five members of the RecQ helicase family, RECQL, WRN, BLM, RTS and RECQL5, have been found in human and three of them (WRN, BLM and RTS) were disclosed to be the genes responsible for Werner, Bloom and Rothmund-Thomson syndromes, respectively. RECQL5 (RecQ helicase protein-like 5) was isolated as the fifth member of the family in humans through a search of homologous expressed sequence tags. The gene is expressed with at least three alternative splicing products, alpha, beta and gamma. Here, we isolated mouse RECQL5 beta and determined the DNA sequence of full-length cDNA as well as the genome organization and chromosome locus. The mouse RECQL5 beta gene consists of 2949 bp coding 982 amino acid residues. Comparison of amino acid sequence among human (Homo sapiens), mouse (Mus musculus), Drosophila melanogaster and Caenorhabditis elegans RECQL5 beta homologs revealed three portions of highly conserved regions in addition to the helicase domain. Nineteen exons are dispersed over 40 kbp in the genome and all of the acceptor and donor sites for the splicing of each exon conform to the GT/AG rule. The gene is localized to the mouse chromosome 11E2, which has a syntenic relation to human 17q25.2-q25.3 where human RECQL5 beta exists. Our genetic characterizations of the mouse RECQL5 beta gene will contribute to functional studies on the RECQL5 beta products.
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Affiliation(s)
- T Ohhata
- Graduate School of Science and Technology, Chiba University, Yayoi-cho 1-33, Inage-ku, Chiba-shi, Chiba 263-8522, Japan
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45
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Mankouri HW, Morgan A. The DNA helicase activity of yeast Sgs1p is essential for normal lifespan but not for resistance to topoisomerase inhibitors. Mech Ageing Dev 2001; 122:1107-20. [PMID: 11389927 DOI: 10.1016/s0047-6374(01)00253-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The Saccharomyces cerevisiae SGS1 gene is a member of the RecQ family of ATP-dependent DNA helicases, which includes the human WRN, BLM and RECQ4 genes. Mutations in the WRN gene cause the human premature ageing disorder, Werner's syndrome. Deletion of the SGS1 gene also causes premature ageing in yeast, suggesting that the molecular mechanisms of cellular ageing may be evolutionarily conserved. To investigate the role of the RecQ helicase domain in ageing, a point mutation (SGS1 K(706)-->A) known to eliminate the DNA helicase activity of Sgs1p was constructed. This mutant allele failed to rescue the premature ageing of the sgs1Delta strain, demonstrating that Sgs1p DNA helicase activity is required for a normal lifespan. In contrast, the SGS1 K(706)-->A allele was sufficient to rescue the hypersensitivity of the sgs1Delta strain to topoisomerase inhibitors, but not other genotoxic agents. These findings support the idea that Sgs1p fulfils multiple cellular functions, and that DNA helicase activity is dispensable for some of these (e.g. functional interaction with topoisomerases), but essential for others (e.g. longevity).
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Affiliation(s)
- H W Mankouri
- Department of Physiology, University of Liverpool, PO Box 147, Crown Street, L69 3BX, Liverpool, UK
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46
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Branzei D, Hayashi T, Suzuki H, Masuko T, Onoda F, Heo SJ, Ikeda H, Shimamoto A, Furuichi Y, Seki M, Enomoto T. A novel protein interacts with the Werner's syndrome gene product physically and functionally. J Biol Chem 2001; 276:20364-9. [PMID: 11301316 DOI: 10.1074/jbc.c100035200] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Werner's syndrome (WS) is a rare autosomal recessive disorder characterized by premature aging. The gene responsible for WS encodes a protein homologous to Escherichia coli RecQ. Here we describe a novel Werner helicase interacting protein (WHIP), which interacts with the N-terminal portion of Werner protein (WRN), containing the exonuclease domain. WHIP, which shows homology to replication factor C family proteins, is conserved from E. coli to human. Ectopically expressed WHIP and WRN co-localized in granular structures in the nucleus. The functional relationship between WHIP and WRN was indicated by genetic analysis of yeast cells. Disruptants of the SGS1 gene of Saccharomyces cerevisiae, which is the WRN homologue in yeast, show an accelerated aging phenotype and high sensitivity to methyl methanesulfonate as compared with wild-type cells. Disruption of the yeast WHIP (yWHIP) gene in wild-type cells and sgs1 disruptants resulted in slightly accelerated aging and enhancement of the premature aging phenotype of sgs1 disruptants, respectively. In contrast, disruption of the yWHIP gene partially alleviated the sensitivity to methyl methanesulfonate of sgs1 disruptants.
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47
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Hachiya Y, Motonaga K, Itoh M, Masuko T, Enomoto T, Sonobe H, Takashima S. Immunohistochemical expression and pathogenesis of BLM in the human brain and visceral organs. Neuropathology 2001; 21:123-8. [PMID: 11396677 DOI: 10.1046/j.1440-1789.2001.00379.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Bloom syndrome (BS) involves the clinical features of telangiectatic erythema, immunodeficiency, and an increased risk for cancer. In order to clarify the pathogenetic significance of the responsible gene, BLM, which encodes a protein possessing homology to Escherichia coli RecQ helicase, the immunohistochemistry of BLM was examined in human brains and visceral organs from fetuses to adults and an adult with BS, using anti-BLM antibodies. Purkinje cells exhibited positive BLM immunoreactivity from 21 gestational weeks (GW), which transiently increased at approximately 40 GW. Neurons of the pontine tegmentum were immunolabeled from the early fetal period. In visceral organs, positive BLM immunoreactivity was observed in the Hassal corpuscles in the thymus from 24 GW, in beta-cells in the Langerhans islets of the pancreas from 36 GW, and in sperm cells and sperms of the testes from 11 years of age. But in a patient with BS, it was negative in the pancreas and testis tissues examined. The characteristic effect of BLM on specific cells in different periods suggests that the BLM gene product is closely related to neuronal development as well as immune, insulin secretory and sperm functions, which appear in different periods, and disorders of which are major symptoms of BS.
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Affiliation(s)
- Y Hachiya
- First Department of Pediatrics, Toho University School of Medicine, Tokyo, Japan
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48
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Kamath-Loeb AS, Loeb LA, Johansson E, Burgers PM, Fry M. Interactions between the Werner syndrome helicase and DNA polymerase delta specifically facilitate copying of tetraplex and hairpin structures of the d(CGG)n trinucleotide repeat sequence. J Biol Chem 2001; 276:16439-46. [PMID: 11279038 DOI: 10.1074/jbc.m100253200] [Citation(s) in RCA: 151] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Werner syndrome (WS) is an inherited disorder characterized by premature aging and genomic instability. The protein encoded by the WS gene, WRN, possesses intrinsic 3' --> 5' DNA helicase and 3' --> 5' DNA exonuclease activities. WRN helicase resolves alternate DNA structures including tetraplex and triplex DNA, and Holliday junctions. Thus, one function of WRN may be to unwind secondary structures that impede cellular DNA transactions. We report here that hairpin and G'2 bimolecular tetraplex structures of the fragile X expanded sequence, d(CGG)(n), effectively impede synthesis by three eukaryotic replicative DNA polymerases (pol): pol alpha, pol delta, and pol epsilon. The constraints imposed on pol delta-catalyzed synthesis are relieved, however, by WRN; WRN facilitates pol delta to traverse these template secondary structures to synthesize full-length DNA products. The alleviatory effect of WRN is limited to pol delta; neither pol alpha nor pol epsilon can traverse template d(CGG)(n) hairpin and tetraplex structures in the presence of WRN. Alleviation of pausing by pol delta is observed with Escherichia coli RecQ but not with UvrD helicase, suggesting a concerted action of RecQ helicases and pol delta. Our findings suggest a possible role of WRN in rescuing pol delta-mediated replication at forks stalled by unusual DNA secondary structures.
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Affiliation(s)
- A S Kamath-Loeb
- Gottstein Memorial Cancer Research Laboratory, Departments of Pathology and Biochemistry, University of Washington, Seattle, Washington 98195, USA.
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49
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Kusano K, Johnson-Schlitz DM, Engels WR. Sterility of Drosophila with mutations in the Bloom syndrome gene--complementation by Ku70. Science 2001; 291:2600-2. [PMID: 11283371 DOI: 10.1126/science.291.5513.2600] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The Drosophila Dmblm locus is a homolog of the human Bloom syndrome gene, which encodes a helicase of the RECQ family. We show that Dmblm is identical to mus309, a locus originally identified in a mutagen-sensitivity screen. One mus309 allele, which carries a stop codon between two of the helicase motifs, causes partial male sterility and complete female sterility. Mutant males produce an excess of XY sperm and nullo sperm, consistent with a high frequency of nondisjunction and/or chromosome loss. These phenotypes of mus309 suggest that Dmblm functions in DNA double-strand break repair. The mutant Dmblm phenotypes were partially rescued by an extra copy of the DNA repair gene Ku70, indicating that the two genes functionally interact in vivo.
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Affiliation(s)
- K Kusano
- Laboratory of Genetics, University of Wisconsin- Madison, Madison, WI 53706, USA
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50
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Imamura O, Fujita K, Shimamoto A, Tanabe H, Takeda S, Furuichi Y, Matsumoto T. Bloom helicase is involved in DNA surveillance in early S phase in vertebrate cells. Oncogene 2001; 20:1143-51. [PMID: 11313858 DOI: 10.1038/sj.onc.1204195] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2000] [Revised: 12/12/2000] [Accepted: 12/19/2000] [Indexed: 11/09/2022]
Abstract
Bloom syndrome (BS) is a recessive human genetic disorder characterized by short stature, immunodeficiency and an elevated risk of malignancy. The gene mutated in BS, BLM, encodes a RecQ-type DNA helicase. BS cells have mutator phenotypes such as hyper-recombination, chromosome instability and an increased frequency of sister chromatid exchange (SCE). To define the primary role of BLM, we generated BLM(-/-) mutants of the chicken B-cell line DT40. In addition to characteristics of BLM(-/-) cells reported previously by the other group, they are hypersensitive to genotoxic agents such as etoposide, bleomycin and 4-nitroquinoline-1-oxide and irradiation with the short wave length of UV (UVC) light, whereas they exhibit normal sensitivity to X-ray irradiation and hydroxyurea. UVC irradiation to BLM(-/-) cells during G(1) to early S phase caused chromosomal instability such as chromatid breaks and chromosomal quadriradials, leading to eventual cell death. These results suggest that BLM is involved in surveillance of base abnormalities in genomic DNA that may be encountered by replication forks in early S phase. Such surveillance would maintain genomic stability in vertebrate cells, resulting in the prevention of cellular tumorigenesis.
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Affiliation(s)
- O Imamura
- AGENE Research Institute, 200 Kajiwara, Kamakura, Kanagawa 247-0063, Japan
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