1
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Adams MC, Schiltz C, Sun J, Hosford C, Johnson V, Pan H, Borbat P, Freed J, Thomason L, Court C, Court D, Chappie J. The crystal structure of bacteriophage λ RexA provides novel insights into the DNA binding properties of Rex-like phage exclusion proteins. Nucleic Acids Res 2024; 52:4659-4675. [PMID: 38554102 PMCID: PMC11077077 DOI: 10.1093/nar/gkae212] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2023] [Revised: 03/07/2024] [Accepted: 03/12/2024] [Indexed: 04/01/2024] Open
Abstract
RexA and RexB function as an exclusion system that prevents bacteriophage T4rII mutants from growing on Escherichia coli λ phage lysogens. Recent data established that RexA is a non-specific DNA binding protein that can act independently of RexB to bias the λ bistable switch toward the lytic state, preventing conversion back to lysogeny. The molecular interactions underlying these activities are unknown, owing in part to a dearth of structural information. Here, we present the 2.05-Å crystal structure of the λ RexA dimer, which reveals a two-domain architecture with unexpected structural homology to the recombination-associated protein RdgC. Modelling suggests that our structure adopts a closed conformation and would require significant domain rearrangements to facilitate DNA binding. Mutagenesis coupled with electromobility shift assays, limited proteolysis, and double electron-electron spin resonance spectroscopy support a DNA-dependent conformational change. In vivo phenotypes of RexA mutants suggest that DNA binding is not a strict requirement for phage exclusion but may directly contribute to modulation of the bistable switch. We further demonstrate that RexA homologs from other temperate phages also dimerize and bind DNA in vitro. Collectively, these findings advance our mechanistic understanding of Rex functions and provide new evolutionary insights into different aspects of phage biology.
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Affiliation(s)
- Myfanwy C Adams
- Department of Molecular Medicine, Cornell University, Ithaca, NY 14853, USA
| | - Carl J Schiltz
- Department of Molecular Medicine, Cornell University, Ithaca, NY 14853, USA
| | - Jing Sun
- Department of Molecular Medicine, Cornell University, Ithaca, NY 14853, USA
| | | | - Virginia M Johnson
- Department of Molecular Medicine, Cornell University, Ithaca, NY 14853, USA
| | - Hao Pan
- Department of Molecular Medicine, Cornell University, Ithaca, NY 14853, USA
| | - Peter P Borbat
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA
- National Biomedical Resource for Advanced Electron Spin Resonance Spectroscopy, Cornell University, Ithaca, NY 14853, USA
| | - Jack H Freed
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA
- National Biomedical Resource for Advanced Electron Spin Resonance Spectroscopy, Cornell University, Ithaca, NY 14853, USA
| | - Lynn C Thomason
- Center for Cancer Research, National Cancer Institute, Frederick, MD21702, USA
| | - Carolyn Court
- Center for Cancer Research, National Cancer Institute, Frederick, MD21702, USA
| | - Donald L Court
- Center for Cancer Research, National Cancer Institute, Frederick, MD21702, USA
| | - Joshua S Chappie
- Department of Molecular Medicine, Cornell University, Ithaca, NY 14853, USA
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2
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von Seth J, van der Valk T, Lord E, Sigeman H, Olsen RA, Knapp M, Kardailsky O, Robertson F, Hale M, Houston D, Kennedy E, Dalén L, Norén K, Massaro M, Robertson BC, Dussex N. Genomic trajectories of a near-extinction event in the Chatham Island black robin. BMC Genomics 2022; 23:747. [DOI: 10.1186/s12864-022-08963-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2022] [Accepted: 10/23/2022] [Indexed: 11/11/2022] Open
Abstract
Abstract
Background
Understanding the micro-evolutionary response of populations to demographic declines is a major goal in evolutionary and conservation biology. In small populations, genetic drift can lead to an accumulation of deleterious mutations, which will increase the risk of extinction. However, demographic recovery can still occur after extreme declines, suggesting that natural selection may purge deleterious mutations, even in extremely small populations. The Chatham Island black robin (Petroica traversi) is arguably the most inbred bird species in the world. It avoided imminent extinction in the early 1980s and after a remarkable recovery from a single pair, a second population was established and the two extant populations have evolved in complete isolation since then. Here, we analysed 52 modern and historical genomes to examine the genomic consequences of this extreme bottleneck and the subsequent translocation.
Results
We found evidence for two-fold decline in heterozygosity and three- to four-fold increase in inbreeding in modern genomes. Moreover, there was partial support for temporal reduction in total load for detrimental variation. In contrast, compared to historical genomes, modern genomes showed a significantly higher realised load, reflecting the temporal increase in inbreeding. Furthermore, the translocation induced only small changes in the frequency of deleterious alleles, with the majority of detrimental variation being shared between the two populations.
Conclusion
Our results highlight the dynamics of mutational load in a species that recovered from the brink of extinction, and show rather limited temporal changes in mutational load. We hypothesise that ancestral purging may have been facilitated by population fragmentation and isolation on several islands for thousands of generations and may have already reduced much of the highly deleterious load well before human arrival and introduction of pests to the archipelago. The majority of fixed deleterious variation was shared between the modern populations, but translocation of individuals with low mutational load could possibly mitigate further fixation of high-frequency deleterious variation.
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3
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Peyrégne S, Peter BM. AuthentiCT: a model of ancient DNA damage to estimate the proportion of present-day DNA contamination. Genome Biol 2020; 21:246. [PMID: 32933569 PMCID: PMC7490890 DOI: 10.1186/s13059-020-02123-y] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2020] [Accepted: 07/27/2020] [Indexed: 12/31/2022] Open
Abstract
Contamination from present-day DNA is a fundamental issue when studying ancient DNA from historical or archaeological material, and quantifying the amount of contamination is essential for downstream analyses. We present AuthentiCT, a command-line tool to estimate the proportion of present-day DNA contamination in ancient DNA datasets generated from single-stranded DNA libraries. The prediction is based solely on the patterns of post-mortem damage observed on ancient DNA sequences. The method has the power to quantify contamination from as few as 10,000 mapped sequences, making it particularly useful for analysing specimens that are poorly preserved or for which little data is available.
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Affiliation(s)
- Stéphane Peyrégne
- Department of Evolutionary Genetics, Max Planck Institute for Evolutionary Anthropology, 04103, Leipzig, Germany.
| | - Benjamin M Peter
- Department of Evolutionary Genetics, Max Planck Institute for Evolutionary Anthropology, 04103, Leipzig, Germany
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4
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Neukamm J, Pfrengle S, Molak M, Seitz A, Francken M, Eppenberger P, Avanzi C, Reiter E, Urban C, Welte B, Stockhammer PW, Teßmann B, Herbig A, Harvati K, Nieselt K, Krause J, Schuenemann VJ. 2000-year-old pathogen genomes reconstructed from metagenomic analysis of Egyptian mummified individuals. BMC Biol 2020; 18:108. [PMID: 32859198 PMCID: PMC7456089 DOI: 10.1186/s12915-020-00839-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2020] [Accepted: 07/29/2020] [Indexed: 12/26/2022] Open
Abstract
BACKGROUND Recent advances in sequencing have facilitated large-scale analyses of the metagenomic composition of different samples, including the environmental microbiome of air, water, and soil, as well as the microbiome of living humans and other animals. Analyses of the microbiome of ancient human samples may provide insights into human health and disease, as well as pathogen evolution, but the field is still in its very early stages and considered highly challenging. RESULTS The metagenomic and pathogen content of Egyptian mummified individuals from different time periods was investigated via genetic analysis of the microbial composition of various tissues. The analysis of the dental calculus' microbiome identified Red Complex bacteria, which are correlated with periodontal diseases. From bone and soft tissue, genomes of two ancient pathogens, a 2200-year-old Mycobacterium leprae strain and a 2000-year-old human hepatitis B virus, were successfully reconstructed. CONCLUSIONS The results show the reliability of metagenomic studies on Egyptian mummified individuals and the potential to use them as a source for the extraction of ancient pathogen DNA.
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Affiliation(s)
- Judith Neukamm
- Institute of Evolutionary Medicine, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.,Institute for Archaeological Sciences, University of Tübingen, Rümelinstrasse 19-23, 72070, Tübingen, Germany.,Institute for Bioinformatics and Medical Informatics, University of Tübingen, Sand 14, 72076, Tübingen, Germany
| | - Saskia Pfrengle
- Institute of Evolutionary Medicine, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.,Institute for Archaeological Sciences, University of Tübingen, Rümelinstrasse 19-23, 72070, Tübingen, Germany
| | - Martyna Molak
- Museum and Institute of Zoology, Polish Academy of Sciences, Wilcza 64, 00-679, Warsaw, Poland.,Centre of New Technologies, University of Warsaw, S. Banacha 2c, 02-097, Warsaw, Poland
| | - Alexander Seitz
- Institute for Bioinformatics and Medical Informatics, University of Tübingen, Sand 14, 72076, Tübingen, Germany
| | - Michael Francken
- Senckenberg Centre for Human Evolution and Paleoenvironments, University of Tübingen, Rümelinstrasse 19-23, 72070, Tübingen, Germany.,Paleoanthropology, Dept. of Geosciences, University of Tübingen, Rümelinstrasse 19-23, 72070, Tübingen, Germany
| | - Partick Eppenberger
- Institute of Evolutionary Medicine, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland
| | - Charlotte Avanzi
- Mycobacteria Research Laboratories, Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, USA
| | - Ella Reiter
- Institute for Archaeological Sciences, University of Tübingen, Rümelinstrasse 19-23, 72070, Tübingen, Germany
| | - Christian Urban
- Institute of Evolutionary Medicine, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland
| | - Beatrix Welte
- Institute of Pre- and Protohistory and Medieval Archaeology, Department of Early Prehistory and Quaternary Ecology, University of Tübingen, Rümelinstrasse 19-23, 72070, Tübingen, Germany
| | - Philipp W Stockhammer
- Institute for Pre- and Protohistoric Archaeology and Archaeology of the Roman Provinces, Ludwig Maximilian University Munich, 80799, Munich, Germany.,Max Planck Institute for the Science of Human History, Kahlaische Str. 10, 07745, Jena, Germany
| | - Barbara Teßmann
- Berlin Society of Anthropology, Ethnology and Prehistory, 10117, Berlin, Germany.,Museum of Prehistory and Early History, SMPK Berlin, 10117, Berlin, Germany
| | - Alexander Herbig
- Max Planck Institute for the Science of Human History, Kahlaische Str. 10, 07745, Jena, Germany
| | - Katerina Harvati
- Senckenberg Centre for Human Evolution and Paleoenvironments, University of Tübingen, Rümelinstrasse 19-23, 72070, Tübingen, Germany.,Paleoanthropology, Dept. of Geosciences, University of Tübingen, Rümelinstrasse 19-23, 72070, Tübingen, Germany.,DFG Centre for Advanced Studies Words, Bones, Genes, Tools: Tracking Linguistic, Cultural and Biological Trajectories of the Human Past, University of Tübingen, Rümelinstrasse 19-23, 72070, Tübingen, Germany
| | - Kay Nieselt
- Institute for Bioinformatics and Medical Informatics, University of Tübingen, Sand 14, 72076, Tübingen, Germany
| | - Johannes Krause
- Institute for Archaeological Sciences, University of Tübingen, Rümelinstrasse 19-23, 72070, Tübingen, Germany. .,Senckenberg Centre for Human Evolution and Paleoenvironments, University of Tübingen, Rümelinstrasse 19-23, 72070, Tübingen, Germany. .,Max Planck Institute for the Science of Human History, Kahlaische Str. 10, 07745, Jena, Germany.
| | - Verena J Schuenemann
- Institute of Evolutionary Medicine, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland. .,Institute for Archaeological Sciences, University of Tübingen, Rümelinstrasse 19-23, 72070, Tübingen, Germany. .,Senckenberg Centre for Human Evolution and Paleoenvironments, University of Tübingen, Rümelinstrasse 19-23, 72070, Tübingen, Germany.
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Biomolecular analyses reveal the age, sex and species identity of a near-intact Pleistocene bird carcass. Commun Biol 2020; 3:84. [PMID: 32081985 PMCID: PMC7035339 DOI: 10.1038/s42003-020-0806-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2019] [Accepted: 01/31/2020] [Indexed: 11/18/2022] Open
Abstract
Ancient remains found in permafrost represent a rare opportunity to study past ecosystems. Here, we present an exceptionally well-preserved ancient bird carcass found in the Siberian permafrost, along with a radiocarbon date and a reconstruction of its complete mitochondrial genome. The carcass was radiocarbon dated to approximately 44–49 ka BP, and was genetically identified as a female horned lark. This is a species that usually inhabits open habitat, such as the steppe environment that existed in Siberia at the time. This near-intact carcass highlights the potential of permafrost remains for evolutionary studies that combine both morphology and ancient nucleic acids. Nicolas Dussex et al. identify a 44,000–49,000 year old bird found in Siberian permafrost as a female horned lark using ancient DNA. This exceptionally well-preserved specimen illustrates the potential contribution to science of permafrost deposits, such as the study of ecology and evolution of ancient ecosystems, calibration of molecular clocks, and furthering our understanding of processes such as biological regulation and gene expression in relation to climate change.
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DNA Packaging and Genomics of the Salmonella 9NA-Like Phages. J Virol 2019; 93:JVI.00848-19. [PMID: 31462565 DOI: 10.1128/jvi.00848-19] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2019] [Accepted: 08/26/2019] [Indexed: 12/14/2022] Open
Abstract
We present the genome sequences of Salmonella enterica tailed phages Sasha, Sergei, and Solent. These phages, along with Salmonella phages 9NA, FSL_SP-062, and FSL_SP-069 and the more distantly related Proteus phage PmiS-Isfahan, have similarly sized genomes of between 52 and 57 kbp in length that are largely syntenic. Their genomes also show substantial genome mosaicism relative to one another, which is common within tailed phage clusters. Their gene content ranges from 80 to 99 predicted genes, of which 40 are common to all seven and form the core genome, which includes all identifiable virion assembly and DNA replication genes. The total number of gene types (pangenome) in the seven phages is 176, and 59 of these are unique to individual phages. Their core genomes are much more closely related to one another than to the genome of any other known phage, and they comprise a well-defined cluster within the family Siphoviridae To begin to characterize this group of phages in more experimental detail, we identified the genes that encode the major virion proteins and examined the DNA packaging of the prototypic member, phage 9NA. We show that it uses a pac site-directed headful packaging mechanism that results in virion chromosomes that are circularly permuted and about 13% terminally redundant. We also show that its packaging series initiates with double-stranded DNA cleavages that are scattered across a 170-bp region and that its headful measuring device has a precision of ±1.8%.IMPORTANCE The 9NA-like phages are clearly highly related to each other but are not closely related to any other known phage type. This work describes the genomes of three new 9NA-like phages and the results of experimental analysis of the proteome of the 9NA virion and DNA packaging into the 9NA phage head. There is increasing interest in the biology of phages because of their potential for use as antibacterial agents and for their ecological roles in bacterial communities. 9NA-like phages that infect two bacterial genera have been identified to date, and related phages infecting additional Gram-negative bacterial hosts are likely to be found in the future. This work provides a foundation for the study of these phages, which will facilitate their study and potential use.
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7
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Zhou B, Wen S, Wang L, Jin L, Li H, Zhang H. AntCaller: an accurate variant caller incorporating ancient DNA damage. Mol Genet Genomics 2017; 292:1419-1430. [DOI: 10.1007/s00438-017-1358-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2017] [Accepted: 08/16/2017] [Indexed: 12/11/2022]
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8
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Devlin R, Marques CA, McCulloch R. Does DNA replication direct locus-specific recombination during host immune evasion by antigenic variation in the African trypanosome? Curr Genet 2017; 63:441-449. [PMID: 27822899 PMCID: PMC5422504 DOI: 10.1007/s00294-016-0662-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2016] [Revised: 10/26/2016] [Accepted: 10/27/2016] [Indexed: 12/14/2022]
Abstract
All pathogens must survive host immune attack and, amongst the survival strategies that have evolved, antigenic variation is a particularly widespread reaction to thwart adaptive immunity. Though the reactions that underlie antigenic variation are highly varied, recombination by gene conversion is a widespread approach to immune survival in bacterial and eukaryotic pathogens. In the African trypanosome, antigenic variation involves gene conversion-catalysed movement of a huge number of variant surface glycoprotein (VSG) genes into a few telomeric sites for VSG expression, amongst which only a single site is actively transcribed at one time. Genetic evidence indicates VSG gene conversion has co-opted the general genome maintenance reaction of homologous recombination, aligning the reaction strategy with targeted rearrangements found in many organisms. What is less clear is how gene conversion might be initiated within the locality of the VSG expression sites. Here, we discuss three emerging models for VSG switching initiation and ask how these compare with processes for adaptive genome change found in other organisms.
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Affiliation(s)
- Rebecca Devlin
- The Wellcome Trust Centre for Molecular Parasitology, Institute of Infection, Immunity and Inflammation, University of Glasgow, Sir Graeme Davis Building, 120 University Place, Glasgow, G12 8TA, UK
| | - Catarina A Marques
- The Wellcome Trust Centre for Molecular Parasitology, Institute of Infection, Immunity and Inflammation, University of Glasgow, Sir Graeme Davis Building, 120 University Place, Glasgow, G12 8TA, UK
- Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dundee, UK
| | - Richard McCulloch
- The Wellcome Trust Centre for Molecular Parasitology, Institute of Infection, Immunity and Inflammation, University of Glasgow, Sir Graeme Davis Building, 120 University Place, Glasgow, G12 8TA, UK.
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Kim CH, Kim YH, Anderson AJ, Kim YC. Proteomic Analysis of a Global Regulator GacS Sensor Kinase in the Rhizobacterium, Pseudomonas chlororaphis O6. THE PLANT PATHOLOGY JOURNAL 2014; 30:220-7. [PMID: 25289007 PMCID: PMC4174846 DOI: 10.5423/ppj.nt.02.2014.0012] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2014] [Revised: 03/26/2014] [Accepted: 03/27/2014] [Indexed: 05/09/2023]
Abstract
The GacS/GacA system in the root colonizer Pseudomonas chlororaphis O6 is a key regulator of many traits relevant to the biocontrol function of this bacterium. Proteomic analysis revealed 12 proteins were down-regulated in a gacS mutant of P. chlororaphis O6. These GacS-regulated proteins functioned in combating oxidative stress, cell signaling, biosynthesis of secondary metabolism, and secretion. The extent of regulation was shown by real-time RT-PCR to vary between the genes. Mutants of P. chlororaphis O6 were generated in two GacS-regulated genes, trpE, encoding a protein involved in tryptophan synthesis, and prnA, required for conversion of tryptophan to the antimicrobial compound, pyrrolitrin. Failure of the trpE mutant to induce systemic resistance in tobacco against a foliar pathogen causing soft rot, Pectobacterium carotovorum SCCI, correlated with reduced colonization of root surfaces implying an inadequate supply of tryptophan to support growth. Although colonization was not affected by mutation in the prnA gene, induction of systemic resistance was reduced, suggesting that pyrrolnitrin was an activator of plant resistance as well as an antifungal agent. Study of mutants in the other GacS-regulated proteins will indicate further the features required for biocontrol-activity in this rhizobacterium.
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Affiliation(s)
- Chul Hong Kim
- Department of Floriculture, Chunnam Techno University, Jeonnam 516-911, Korea
| | - Yong Hwan Kim
- Korea Institute of Planning & Evaluation for Technology on Food, Agriculture, Forestry & Fisheries, Anyang 431-060, Korea
| | - Anne J. Anderson
- Department of Biology, Utah State University, Logan, Utah 843220-5305, USA
| | - Young Cheol Kim
- Institute of Environmentally-Friendly Agriculture, Chonnam National University, Gwangju 500-757, Korea
- Corresponding author. Phone) +82-62-530-2071, FAX) +82-62-530-2079, E-mail)
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Arslan Z, Wurm R, Brener O, Ellinger P, Nagel-Steger L, Oesterhelt F, Schmitt L, Willbold D, Wagner R, Gohlke H, Smits SHJ, Pul U. Double-strand DNA end-binding and sliding of the toroidal CRISPR-associated protein Csn2. Nucleic Acids Res 2013; 41:6347-59. [PMID: 23625968 PMCID: PMC3695520 DOI: 10.1093/nar/gkt315] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The adaptive immunity of bacteria against foreign nucleic acids, mediated by CRISPR (clustered regularly interspaced short palindromic repeats), relies on the specific incorporation of short pieces of the invading foreign DNA into a special genomic locus, termed CRISPR array. The stored sequences (spacers) are subsequently used in the form of small RNAs (crRNAs) to interfere with the target nucleic acid. We explored the DNA-binding mechanism of the immunization protein Csn2 from the human pathogen Streptococcus agalactiae using different biochemical techniques, atomic force microscopic imaging and molecular dynamics simulations. The results demonstrate that the ring-shaped Csn2 tetramer binds DNA ends through its central hole and slides inward, likely by a screw motion along the helical path of the enclosed DNA. The presented data indicate an accessory function of Csn2 during integration of exogenous DNA by end-joining.
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Affiliation(s)
- Zihni Arslan
- Institut für Physikalische Biologie, Heinrich-Heine-Universität, Universitätsstr. 1, 40225 Düsseldorf, Germany
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Uranga LA, Balise VD, Benally CV, Grey A, Lusetti SL. The Escherichia coli DinD protein modulates RecA activity by inhibiting postsynaptic RecA filaments. J Biol Chem 2011; 286:29480-91. [PMID: 21697094 DOI: 10.1074/jbc.m111.245373] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Escherichia coli dinD is an SOS gene up-regulated in response to DNA damage. We find that the purified DinD protein is a novel inhibitor of RecA-mediated DNA strand exchange activities. Most modulators of RecA protein activity act by controlling the amount of RecA protein bound to single-stranded DNA by affecting either the loading of RecA protein onto DNA or the disassembly of RecA nucleoprotein filaments bound to single-stranded DNA. The DinD protein, however, acts postsynaptically to inhibit RecA during an on-going DNA strand exchange, likely through the disassembly of RecA filaments. DinD protein does not affect RecA single-stranded DNA filaments but efficiently disassembles RecA when bound to two or more DNA strands, effectively halting RecA-mediated branch migration. By utilizing a nonspecific duplex DNA-binding protein, YebG, we show that the DinD effect is not simply due to duplex DNA sequestration. We present a model suggesting that the negative effects of DinD protein are targeted to a specific conformational state of the RecA protein and discuss the potential role of DinD protein in the regulation of recombinational DNA repair.
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Affiliation(s)
- Lee A Uranga
- Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, New Mexico 88003, USA
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