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Arbel-Groissman M, Menuhin-Gruman I, Yehezkeli H, Naki D, Bergman S, Udi Y, Tuller T. The Causes for Genomic Instability and How to Try and Reduce Them Through Rational Design of Synthetic DNA. Methods Mol Biol 2024; 2760:371-392. [PMID: 38468099 DOI: 10.1007/978-1-0716-3658-9_21] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/13/2024]
Abstract
Genetic engineering has revolutionized our ability to manipulate DNA and engineer organisms for various applications. However, this approach can lead to genomic instability, which can result in unwanted effects such as toxicity, mutagenesis, and reduced productivity. To overcome these challenges, smart design of synthetic DNA has emerged as a promising solution. By taking into consideration the intricate relationships between gene expression and cellular metabolism, researchers can design synthetic constructs that minimize metabolic stress on the host cell, reduce mutagenesis, and increase protein yield. In this chapter, we summarize the main challenges of genomic instability in genetic engineering and address the dangers of unknowingly incorporating genomically unstable sequences in synthetic DNA. We also demonstrate the instability of those sequences by the fact that they are selected against conserved sequences in nature. We highlight the benefits of using ESO, a tool for the rational design of DNA for avoiding genetically unstable sequences, and also summarize the main principles and working parameters of the software that allow maximizing its benefits and impact.
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Affiliation(s)
- Matan Arbel-Groissman
- Shmunis School of Biomedicine and Cancer Research, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
| | - Itamar Menuhin-Gruman
- School of Mathematical Sciences, The Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv, Israel
| | - Hader Yehezkeli
- Department of Biomedical Engineering, Tel Aviv University, Tel Aviv, Israel
| | - Doron Naki
- Shmunis School of Biomedicine and Cancer Research, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
| | - Shaked Bergman
- Department of Biomedical Engineering, Tel Aviv University, Tel Aviv, Israel
| | - Yarin Udi
- Department of Biomedical Engineering, Tel Aviv University, Tel Aviv, Israel
| | - Tamir Tuller
- Department of Biomedical Engineering, Tel Aviv University, Tel Aviv, Israel.
- The Sagol School of Neuroscience, Tel-Aviv University, Tel Aviv, Israel.
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2
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Henry C, Kaur G, Cherry ME, Henrikus SS, Bonde N, Sharma N, Beyer H, Wood EA, Chitteni-Pattu S, van Oijen A, Robinson A, Cox M. RecF protein targeting to post-replication (daughter strand) gaps II: RecF interaction with replisomes. Nucleic Acids Res 2023; 51:5714-5742. [PMID: 37125644 PMCID: PMC10287930 DOI: 10.1093/nar/gkad310] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2022] [Revised: 04/09/2023] [Accepted: 04/27/2023] [Indexed: 05/02/2023] Open
Abstract
The bacterial RecF, RecO, and RecR proteins are an epistasis group involved in loading RecA protein into post-replication gaps. However, the targeting mechanism that brings these proteins to appropriate gaps is unclear. Here, we propose that targeting may involve a direct interaction between RecF and DnaN. In vivo, RecF is commonly found at the replication fork. Over-expression of RecF, but not RecO or a RecF ATPase mutant, is extremely toxic to cells. We provide evidence that the molecular basis of the toxicity lies in replisome destabilization. RecF over-expression leads to loss of genomic replisomes, increased recombination associated with post-replication gaps, increased plasmid loss, and SOS induction. Using three different methods, we document direct interactions of RecF with the DnaN β-clamp and DnaG primase that may underlie the replisome effects. In a single-molecule rolling-circle replication system in vitro, physiological levels of RecF protein trigger post-replication gap formation. We suggest that the RecF interactions, particularly with DnaN, reflect a functional link between post-replication gap creation and gap processing by RecA. RecF's varied interactions may begin to explain how the RecFOR system is targeted to rare lesion-containing post-replication gaps, avoiding the potentially deleterious RecA loading onto thousands of other gaps created during replication.
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Affiliation(s)
- Camille Henry
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI53706-1544, USA
| | - Gurleen Kaur
- Molecular Horizons Institute and School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, Australia
- Illawarra Health and Medical Research Institute, Wollongong, Australia
| | - Megan E Cherry
- Molecular Horizons Institute and School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, Australia
- Illawarra Health and Medical Research Institute, Wollongong, Australia
| | - Sarah S Henrikus
- Molecular Horizons Institute and School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, Australia
- Illawarra Health and Medical Research Institute, Wollongong, Australia
| | - Nina J Bonde
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI53706-1544, USA
| | - Nischal Sharma
- Molecular Horizons Institute and School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, Australia
- Illawarra Health and Medical Research Institute, Wollongong, Australia
| | - Hope A Beyer
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI53706-1544, USA
| | - Elizabeth A Wood
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI53706-1544, USA
| | - Sindhu Chitteni-Pattu
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI53706-1544, USA
| | - Antoine M van Oijen
- Molecular Horizons Institute and School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, Australia
- Illawarra Health and Medical Research Institute, Wollongong, Australia
| | - Andrew Robinson
- Molecular Horizons Institute and School of Chemistry and Molecular Bioscience, University of Wollongong, Wollongong, Australia
- Illawarra Health and Medical Research Institute, Wollongong, Australia
| | - Michael M Cox
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI53706-1544, USA
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3
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Unbridled Integrons: A Matter of Host Factors. Cells 2022; 11:cells11060925. [PMID: 35326376 PMCID: PMC8946536 DOI: 10.3390/cells11060925] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2022] [Revised: 03/03/2022] [Accepted: 03/04/2022] [Indexed: 12/29/2022] Open
Abstract
Integrons are powerful recombination systems found in bacteria, which act as platforms capable of capturing, stockpiling, excising and reordering mobile elements called cassettes. These dynamic genetic machineries confer a very high potential of adaptation to their host and have quickly found themselves at the forefront of antibiotic resistance, allowing for the quick emergence of multi-resistant phenotypes in a wide range of bacterial species. Part of the success of the integron is explained by its ability to integrate various environmental and biological signals in order to allow the host to respond to these optimally. In this review, we highlight the substantial interconnectivity that exists between integrons and their hosts and its importance to face changing environments. We list the factors influencing the expression of the cassettes, the expression of the integrase, and the various recombination reactions catalyzed by the integrase. The combination of all these host factors allows for a very tight regulation of the system at the cost of a limited ability to spread by horizontal gene transfer and function in remotely related hosts. Hence, we underline the important consequences these factors have on the evolution of integrons. Indeed, we propose that sedentary chromosomal integrons that were less connected or connected via more universal factors are those that have been more successful upon mobilization in mobile genetic structures, in contrast to those that were connected to species-specific host factors. Thus, the level of specificity of the involved host factors network may have been decisive for the transition from chromosomal integrons to the mobile integrons, which are now widespread. As such, integrons represent a perfect example of the conflicting relationship between the ability to control a biological system and its potential for transferability.
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4
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Näsvall J. Dup-In and DIRex: Techniques for Single-Step, Scar-Free Mutagenesis with Marker Recycling. Methods Mol Biol 2022; 2479:85-104. [PMID: 35583734 DOI: 10.1007/978-1-0716-2233-9_7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
This chapter describes two related recombineering-based techniques: "Duplication Insertion" (Dup-In) and "Direct- and Inverted Repeat stimulated excision" (DIRex). Dup-In is used for transferring existing mutations between strains, and DIRex for generating almost any type of mutation. Both techniques use intermediate insertions with counter-selectable cassettes, flanked by directly repeated sequences that enable exact and spontaneous excision of the cassettes. These constructs can be transferred to other strains using generalized transductions, and the final intended mutation is obtained following selection for spontaneous loss of the counter-selectable cassette, which leaves only the intended mutation behind in the final strain. The techniques have been used in several strains of Escherichia coli and Salmonella enterica, and should be readily adaptable to other organisms where λ Red recombineering or similar methods are available.
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Affiliation(s)
- Joakim Näsvall
- Department of Medical Biochemistry and Microbiology, Uppsala University, Uppsala, Sweden.
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5
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Protein innovation through template switching in the Saccharomyces cerevisiae lineage. Sci Rep 2021; 11:22558. [PMID: 34799587 PMCID: PMC8604942 DOI: 10.1038/s41598-021-01736-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2021] [Accepted: 10/27/2021] [Indexed: 11/08/2022] Open
Abstract
DNA polymerase template switching between short, non-identical inverted repeats (IRs) is a genetic mechanism that leads to the homogenization of IR arms and to IR spacer inversion, which cause multinucleotide mutations (MNMs). It is unknown if and how template switching affects gene evolution. In this study, we performed a phylogenetic analysis to determine the effect of template switching between IR arms on coding DNA of Saccharomyces cerevisiae. To achieve this, perfect IRs that co-occurred with MNMs between a strain and its parental node were identified in S. cerevisiae strains. We determined that template switching introduced MNMs into 39 protein-coding genes through S. cerevisiae evolution, resulting in both arm homogenization and inversion of the IR spacer. These events in turn resulted in nonsynonymous substitutions and up to five neighboring amino acid replacements in a single gene. The study demonstrates that template switching is a powerful generator of multiple substitutions within codons. Additionally, some template switching events occurred more than once during S. cerevisiae evolution. Our findings suggest that template switching constitutes a general mutagenic mechanism that results in both nonsynonymous substitutions and parallel evolution, which are traditionally considered as evidence for positive selection, without the need for adaptive explanations.
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6
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Al-Zain AM, Symington LS. The dark side of homology-directed repair. DNA Repair (Amst) 2021; 106:103181. [PMID: 34311272 DOI: 10.1016/j.dnarep.2021.103181] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2021] [Revised: 07/16/2021] [Accepted: 07/16/2021] [Indexed: 10/20/2022]
Abstract
DNA double strand breaks (DSB) are cytotoxic lesions that can lead to genome rearrangements and genomic instability, which are hallmarks of cancer. The two main DSB repair pathways are non-homologous end joining and homologous recombination (HR). While HR is generally highly accurate, it has the potential for rearrangements that occur directly or through intermediates generated during the repair process. Whole genome sequencing of cancers has revealed numerous types of structural rearrangement signatures that are often indicative of repair mediated by sequence homology. However, it can be challenging to delineate repair mechanisms from sequence analysis of rearrangement end products from cancer genomes, or even model systems, because the same rearrangements can be generated by different pathways. Here, we review homology-directed repair pathways and their consequences. Exploring those pathways can lead to a greater understanding of rearrangements that occur in cancer cells.
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Affiliation(s)
- Amr M Al-Zain
- Program in Biological Sciences, Columbia University, New York, NY, 10027, United States; Department of Microbiology & Immunology, Columbia University Irving Medical Center, New York, NY, 10032, United States
| | - Lorraine S Symington
- Department of Microbiology & Immunology, Columbia University Irving Medical Center, New York, NY, 10032, United States; Department of Genetics & Development, Columbia University Irving Medical Center, New York, NY, 10032, United States.
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7
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Jain K, Wood EA, Romero ZJ, Cox MM. RecA-independent recombination: Dependence on the Escherichia coli RarA protein. Mol Microbiol 2021; 115:1122-1137. [PMID: 33247976 PMCID: PMC8160026 DOI: 10.1111/mmi.14655] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2020] [Revised: 10/29/2020] [Accepted: 11/20/2020] [Indexed: 11/30/2022]
Abstract
Most, but not all, homologous genetic recombination in bacteria is mediated by the RecA recombinase. The mechanistic origin of RecA-independent recombination has remained enigmatic. Here, we demonstrate that the RarA protein makes a major enzymatic contribution to RecA-independent recombination. In particular, RarA makes substantial contributions to intermolecular recombination and to recombination events involving relatively short (<200 bp) homologous sequences, where RecA-mediated recombination is inefficient. The effects are seen here in plasmid-based recombination assays and in vivo cloning processes. Vestigial levels of recombination remain even when both RecA and RarA are absent. Additional pathways for RecA-independent recombination, possibly mediated by helicases, are suppressed by exonucleases ExoI and RecJ. Translesion DNA polymerases may also contribute. Our results provide additional substance to a previous report of a functional overlap between RecA and RarA.
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Affiliation(s)
- Kanika Jain
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI, USA
| | - Elizabeth A Wood
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI, USA
| | - Zachary J Romero
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI, USA
| | - Michael M Cox
- Department of Biochemistry, University of Wisconsin-Madison, Madison, WI, USA
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8
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Abstract
Recombineering inserts PCR products into DNA using homologous recombination. A pair of short homology arms (50 base pairs) on the ends of a PCR cassette target the cassette to its intended location. These homology arms can be easily introduced as 5' primer overhangs during the PCR reaction. The flexibility to choose almost any pair of homology arms enables the precise modification of virtually any DNA for purposes of sequence deletion, replacement, insertion, or point mutation. Recombineering often offers significant advantages relative to previous homologous recombination methods that require the construction of cassettes with large homology arms, and relative to traditional cloning methods that become intractable for large plasmids or DNA sequences. However, the tremendous number of variables, options, and pitfalls that can be encountered when designing and performing a recombineering protocol for the first time introduce barriers that can make recombineering a challenging technique for new users to adopt. This article focuses on three recombineering protocols we have found to be particularly robust, providing a detailed guide for choosing the simplest recombineering method for a given application and for performing and troubleshooting experiments. © 2019 by John Wiley & Sons, Inc.
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Affiliation(s)
- Louis J Papa
- Massachusetts Institute of Technology, Department of Chemistry, Cambridge, Massachusetts
| | - Matthew D Shoulders
- Massachusetts Institute of Technology, Department of Chemistry, Cambridge, Massachusetts
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9
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Emergence of Oxacillin Resistance in Stealth Methicillin-Resistant Staphylococcus aureus Due to mecA Sequence Instability. Antimicrob Agents Chemother 2019; 63:AAC.00558-19. [PMID: 31109981 PMCID: PMC6658785 DOI: 10.1128/aac.00558-19] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2019] [Accepted: 05/14/2019] [Indexed: 11/24/2022] Open
Abstract
Staphylococcus aureus strains that possess a mecA gene but are phenotypically susceptible to oxacillin and cefoxitin (OS-MRSA) have been recognized for over a decade and are a challenge for diagnostic laboratories. The mechanisms underlying the discrepancy vary from isolate to isolate. Staphylococcus aureus strains that possess a mecA gene but are phenotypically susceptible to oxacillin and cefoxitin (OS-MRSA) have been recognized for over a decade and are a challenge for diagnostic laboratories. The mechanisms underlying the discrepancy vary from isolate to isolate. We characterized seven OS-MRSA clinical isolates of six different spa types from six different states by whole-genome sequencing to identify the nucleotide sequence changes leading to the OS-MRSA phenotype. The results demonstrated that oxacillin susceptibility was associated with mutations in regions of nucleotide repeats within mecA. Subinhibitory antibiotic exposure selected for secondary mecA mutations that restored oxacillin resistance. Thus, strains of S. aureus that contain mecA but are phenotypically susceptible can become resistant after antibiotic exposure, which may result in treatment failure. OS-MRSA warrant follow-up susceptibility testing to ensure detection of resistant revertants.
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10
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Whole Genome Sequence Analysis of Mutations Accumulated in rad27Δ Yeast Strains with Defects in the Processing of Okazaki Fragments Indicates Template-Switching Events. G3-GENES GENOMES GENETICS 2017; 7:3775-3787. [PMID: 28974572 PMCID: PMC5677150 DOI: 10.1534/g3.117.300262] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
Okazaki fragments that are formed during lagging strand DNA synthesis include an initiating primer consisting of both RNA and DNA. The RNA fragment must be removed before the fragments are joined. In Saccharomyces cerevisiae, a key player in this process is the structure-specific flap endonuclease, Rad27p (human homolog FEN1). To obtain a genomic view of the mutational consequence of loss of RAD27, a S. cerevisiae rad27Δ strain was subcultured for 25 generations and sequenced using Illumina paired-end sequencing. Out of the 455 changes observed in 10 colonies isolated the two most common types of events were insertions or deletions (INDELs) in simple sequence repeats (SSRs) and INDELs mediated by short direct repeats. Surprisingly, we also detected a previously neglected class of 21 template-switching events. These events were presumably generated by quasi-palindrome to palindrome correction, as well as palindrome elongation. The formation of these events is best explained by folding back of the stalled nascent strand and resumption of DNA synthesis using the same nascent strand as a template. Evidence of quasi-palindrome to palindrome correction that could be generated by template switching appears also in yeast genome evolution. Out of the 455 events, 55 events appeared in multiple isolates; further analysis indicates that these loci are mutational hotspots. Since Rad27 acts on the lagging strand when the leading strand should not contain any gaps, we propose a mechanism favoring intramolecular strand switching over an intermolecular mechanism. We note that our results open new ways of understanding template switching that occurs during genome instability and evolution.
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11
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Näsvall J. Direct and Inverted Repeat stimulated excision (DIRex): Simple, single-step, and scar-free mutagenesis of bacterial genes. PLoS One 2017; 12:e0184126. [PMID: 28854250 PMCID: PMC5576700 DOI: 10.1371/journal.pone.0184126] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2017] [Accepted: 08/18/2017] [Indexed: 11/29/2022] Open
Abstract
The need for generating precisely designed mutations is common in genetics, biochemistry, and molecular biology. Here, I describe a new λ Red recombineering method (Direct and Inverted Repeat stimulated excision; DIRex) for fast and easy generation of single point mutations, small insertions or replacements as well as deletions of any size, in bacterial genes. The method does not leave any resistance marker or scar sequence and requires only one transformation to generate a semi-stable intermediate insertion mutant. Spontaneous excision of the intermediate efficiently and accurately generates the final mutant. In addition, the intermediate is transferable between strains by generalized transductions, enabling transfer of the mutation into multiple strains without repeating the recombineering step. Existing methods that can be used to accomplish similar results are either (i) more complicated to design, (ii) more limited in what mutation types can be made, or (iii) require expression of extrinsic factors in addition to λ Red. I demonstrate the utility of the method by generating several deletions, small insertions/replacements, and single nucleotide exchanges in Escherichia coli and Salmonella enterica. Furthermore, the design parameters that influence the excision frequency and the success rate of generating desired point mutations have been examined to determine design guidelines for optimal efficiency.
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Affiliation(s)
- Joakim Näsvall
- Department of Medical Biochemistry and Microbiology, Uppsala University, Uppsala, Sweden
- * E-mail:
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12
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Abstract
Replication forks frequently are challenged by lesions on the DNA template, replication-impeding DNA secondary structures, tightly bound proteins or nucleotide pool imbalance. Studies in bacteria have suggested that under these circumstances the fork may leave behind single-strand DNA gaps that are subsequently filled by homologous recombination, translesion DNA synthesis or template-switching repair synthesis. This review focuses on the template-switching pathways and how the mechanisms of these processes have been deduced from biochemical and genetic studies. I discuss how template-switching can contribute significantly to genetic instability, including mutational hotspots and frequent genetic rearrangements, and how template-switching may be elicited by replication fork damage.
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Affiliation(s)
- Susan T Lovett
- Department of Biology and Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, MA, 2454-9110, USA.
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13
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Influence of IS 256 on Genome Variability and Formation of Small-Colony Variants in Staphylococcus aureus. Antimicrob Agents Chemother 2017; 61:AAC.00144-17. [PMID: 28584147 DOI: 10.1128/aac.00144-17] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2017] [Accepted: 05/30/2017] [Indexed: 12/12/2022] Open
Abstract
Staphylococcus aureus has acquired resistance to nearly all antibiotics used in clinical practice. Whereas some resistance mechanisms are conferred by uptake of resistance genes, others evolve by mutation. In this study, IS256 has been shown to play a role, e.g., in S. aureus strains displaying intermediate resistance to vancomycin (VISA). To characterize the IS256 insertion sites in the genomes of two closely related sequence type 247 (ST247) VISA strains, all insertions were mapped in both VISA and a susceptible control strain. The results showed that the three ST247 strains contained the highest number so far of IS256 insertions for all sequenced S. aureus strains. Furthermore, in contrast to the case with the other IS elements in these genomes, the IS256 insertion sites were not identical in the closely related strains, indicating a high transposition frequency of IS256 When IS256 was introduced into a laboratory strain which was then cultured in the presence of antibiotics, it was possible to isolate small-colony variants (SCVs) that possessed IS256 insertions in guaA and hemY that displayed increased resistance to vancomycin and aminoglycosides, respectively. For these clones, a very rapid reversion to the wild type that resembled the fast reversion of clinical SCVs was observed. The reversion was caused by excision of IS256 in a small number of fast-growing clones that quickly outcompeted the SCVs in broth cultures. In conclusion, the presence of IS256 confers a strong genomic plasticity that is useful for adaptation to antibiotic stress.
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14
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Abstract
DNA repair is essential to maintain genomic integrity and initiate genetic diversity. While gene conversion and classical nonhomologous end-joining are the most physiologically predominant forms of DNA repair mechanisms, emerging lines of evidence suggest the usage of several noncanonical homology-directed repair (HDR) pathways in both prokaryotes and eukaryotes in different contexts. Here we review how these alternative HDR pathways are executed, specifically focusing on the determinants that dictate competition between them and their relevance to cancers that display complex genomic rearrangements or maintain their telomeres by homology-directed DNA synthesis.
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15
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Clayton AL, Jackson DG, Weiss RB, Dale C. Adaptation by Deletogenic Replication Slippage in a Nascent Symbiont. Mol Biol Evol 2016; 33:1957-66. [PMID: 27189544 PMCID: PMC4948707 DOI: 10.1093/molbev/msw071] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
As a consequence of population level constraints in the obligate, host-associated lifestyle, intracellular symbiotic bacteria typically exhibit high rates of molecular sequence evolution and extensive genome degeneration over the course of their host association. While the rationale for genome degeneration is well understood, little is known about the molecular mechanisms driving this change. To understand these mechanisms we compared the genome of Sodalis praecaptivus, a nonhost associated bacterium that is closely related to members of the Sodalis-allied clade of insect endosymbionts, with the very recently derived insect symbiont Candidatus Sodalis pierantonius. The characterization of indel mutations in the genome of Ca. Sodalis pierantonius shows that the replication system in this organism is highly prone to deletions resulting from polymerase slippage events in regions encoding G+C-rich repetitive sequences. This slippage-prone phenotype is mechanistically associated with the loss of certain components of the bacterial DNA recombination machinery at an early stage in symbiotic life and is expected to facilitate rapid adaptation to the novel host environment. This is analogous to the emergence of mutator strains in both natural and laboratory populations of bacteria, which tend to reach high frequencies in clonal populations due to linkage between the mutator allele and the resulting adaptive mutations.
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Affiliation(s)
| | | | | | - Colin Dale
- Department of Biology, University of Utah
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16
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Lai PJ, Lim CT, Le HP, Katayama T, Leach DRF, Furukohri A, Maki H. Long inverted repeat transiently stalls DNA replication by forming hairpin structures on both leading and lagging strands. Genes Cells 2016; 21:136-45. [PMID: 26738888 DOI: 10.1111/gtc.12326] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2015] [Accepted: 11/18/2015] [Indexed: 11/27/2022]
Abstract
Long inverted repeats (LIRs), often found in eukaryotic genomes, are unstable in Escherichia coli where they are recognized by the SbcCD (the bacterial Mre11/Rad50 homologue), an endonuclease/exonuclease capable of cleaving hairpin DNA. It has long been postulated that LIRs form hairpin structures exclusively on the lagging-strand template during DNA replication, and SbcCD cleaves these hairpin-containing lagging strands to generate DNA double-strand breaks. Using a reconstituted oriC plasmid DNA replication system, we have examined how a replication fork behaves when it meets a LIR on DNA. We have shown that leading-strand synthesis stalls transiently within the upstream half of the LIR. Pausing of lagging-strand synthesis at the LIR was not clearly observed, but the pattern of priming sites for Okazaki fragment synthesis was altered within the downstream half of the LIR. We have found that the LIR on a replicating plasmid was cleaved by SbcCD with almost equal frequency on both the leading- and lagging-strand templates. These data strongly suggest that the LIR is readily converted to a cruciform DNA, before the arrival of the fork, creating SbcCD-sensitive hairpin structures on both leading and lagging strands. We propose a model for the replication-dependent extrusion of LIRs to form cruciform structures that transiently impede replication fork movement.
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Affiliation(s)
- Pey Jiun Lai
- Division of Systems Biology, Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara, 630-0192, Japan
| | - Chew Theng Lim
- Division of Systems Biology, Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara, 630-0192, Japan
| | - Hang Phuong Le
- Division of Systems Biology, Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara, 630-0192, Japan
| | - Tsutomu Katayama
- Department of Molecular Biology, Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka, 812-8582, Japan
| | - David R F Leach
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, Kings Buildings, Edinburgh, EH9 3JR, UK
| | - Asako Furukohri
- Division of Systems Biology, Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara, 630-0192, Japan
| | - Hisaji Maki
- Division of Systems Biology, Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara, 630-0192, Japan
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17
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Ithurbide S, Bentchikou E, Coste G, Bost B, Servant P, Sommer S. Single Strand Annealing Plays a Major Role in RecA-Independent Recombination between Repeated Sequences in the Radioresistant Deinococcus radiodurans Bacterium. PLoS Genet 2015; 11:e1005636. [PMID: 26517555 PMCID: PMC4627823 DOI: 10.1371/journal.pgen.1005636] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2015] [Accepted: 10/08/2015] [Indexed: 11/18/2022] Open
Abstract
The bacterium Deinococcus radiodurans is one of the most radioresistant organisms known. It is able to reconstruct a functional genome from hundreds of radiation-induced chromosomal fragments. Our work aims to highlight the genes involved in recombination between 438 bp direct repeats separated by intervening sequences of various lengths ranging from 1,479 bp to 10,500 bp to restore a functional tetA gene in the presence or absence of radiation-induced DNA double strand breaks. The frequency of spontaneous deletion events between the chromosomal direct repeats were the same in recA+ and in ΔrecA, ΔrecF, and ΔrecO bacteria, whereas recombination between chromosomal and plasmid DNA was shown to be strictly dependent on the RecA and RecF proteins. The presence of mutations in one of the repeated sequence reduced, in a MutS-dependent manner, the frequency of the deletion events. The distance between the repeats did not influence the frequencies of deletion events in recA+ as well in ΔrecA bacteria. The absence of the UvrD protein stimulated the recombination between the direct repeats whereas the absence of the DdrB protein, previously shown to be involved in DNA double strand break repair through a single strand annealing (SSA) pathway, strongly reduces the frequency of RecA- (and RecO-) independent deletions events. The absence of the DdrB protein also increased the lethal sectoring of cells devoid of RecA or RecO protein. γ-irradiation of recA+ cells increased about 10-fold the frequencies of the deletion events, but at a lesser extend in cells devoid of the DdrB protein. Altogether, our results suggest a major role of single strand annealing in DNA repeat deletion events in bacteria devoid of the RecA protein, and also in recA+ bacteria exposed to ionizing radiation. Deinococcus radiodurans is known for its exceptional ability to tolerate exposure to DNA damaging agents and, in particular, to very high doses of ionizing radiation. This exceptional radioresistance results from many features including efficient DNA double strand break repair. Here, we examine genome stability in D. radiodurans before and after exposure to ionizing radiation. Rearrangements between repeated sequences are a major source of genome instability and can be deleterious to the organism. Thus, we measured the frequency of recombination between direct repeats separated by intervening sequences of various lengths in the presence or absence of radiation-induced DNA double strand breaks. Strikingly, we showed that the frequency of deletions was as high in strains devoid of the RecA, RecF or RecO proteins as in wild type bacteria, suggesting a very efficient RecA-independent process able to generate genome rearrangements. Our results suggest that single strand annealing may play a major role in genome instability in the absence of homologous recombination.
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Affiliation(s)
- Solenne Ithurbide
- Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Université Paris-Sud, Université Paris-Saclay, Gif sur Yvette, France
| | - Esma Bentchikou
- Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Université Paris-Sud, Université Paris-Saclay, Gif sur Yvette, France
| | - Geneviève Coste
- Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Université Paris-Sud, Université Paris-Saclay, Gif sur Yvette, France
| | - Bruno Bost
- Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Université Paris-Sud, Université Paris-Saclay, Gif sur Yvette, France
| | - Pascale Servant
- Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Université Paris-Sud, Université Paris-Saclay, Gif sur Yvette, France
| | - Suzanne Sommer
- Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Université Paris-Sud, Université Paris-Saclay, Gif sur Yvette, France
- * E-mail:
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Proulx MK, Palace SG, Gandra S, Torres B, Weir S, Stiles T, Ellison RT, Goguen JD. Reversion From Methicillin Susceptibility to Methicillin Resistance in Staphylococcus aureus During Treatment of Bacteremia. J Infect Dis 2015; 213:1041-8. [PMID: 26503983 DOI: 10.1093/infdis/jiv512] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2015] [Accepted: 10/14/2015] [Indexed: 11/12/2022] Open
Abstract
Approximately 3% of Staphylococcus aureus strains that, according to results of conventional phenotypic methods, are highly susceptible to methicillin-like antibiotics also have polymerase chain reaction (PCR) results positive for mecA. The genetic nature of these mecA-positive methicillin-susceptible S. aureus (MSSA) strains has not been investigated. We report the first clearly defined case of reversion from methicillin susceptibility to methicillin resistance among mecA-positive MSSA within a patient during antibiotic therapy. We describe the mechanism of reversion for this strain and for a second clinical isolate that reverts at a similar frequency. The rates of reversion are of the same order of magnitude as spontaneous resistance to drugs like rifampicin. When mecA is detected by PCR in the clinical laboratory, current guidelines recommend that these strains be reported as resistant. Because combination therapy using both a β-lactam and a second antibiotic suppressing the small revertant population may be superior to alternatives such as vancomycin, the benefits of distinguishing between mecA-positive MSSA and MRSA in clinical reports should be evaluated.
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Affiliation(s)
| | | | | | - Brenda Torres
- Clinical Microbiology Laboratory, University of Massachusetts Medical School, Worcester
| | - Susan Weir
- Section of Infectious Diseases, Department of Medicine, Boston University
| | - Tracy Stiles
- Massachusetts Department of Public Health, Jamaica Plain, Massachusetts
| | - Richard T Ellison
- Department of Microbiology and Physiological Systems Division of Infectious Disease
| | - Jon D Goguen
- Department of Microbiology and Physiological Systems
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Lee JH, Jeong DW. Characterization of Mobile Staphylococcus equorum Plasmids Isolated from Fermented Seafood That Confer Lincomycin Resistance. PLoS One 2015; 10:e0140190. [PMID: 26448648 PMCID: PMC4598088 DOI: 10.1371/journal.pone.0140190] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2015] [Accepted: 09/22/2015] [Indexed: 12/18/2022] Open
Abstract
The complete nucleotide sequences of lincomycin-resistance gene (lnuA)-containing plasmids in Staphylococcus equorum strains isolated from the high-salt-fermented seafood jeotgal were determined. These plasmids, designated pSELNU1–3, are 2638-bp long, have two polymorphic sites, and encode typical elements found in plasmids that replicate via a rolling-circle mechanism including the replication protein gene (rep), a double-stranded origin of replication, a single-stranded origin of replication, and counter-transcribed RNA sequence, as well as lnuA. Plasmid sequences exhibit over 83% identity to other Staphylococcus plasmids that harbor rep and lnuA genes. Further, three pairs of identified direct repeats may be involved in inter-plasmid recombination. One plasmid, pSELNU1, was successfully transferred to other Staphylococcus species, Enterococcus faecalis, and Tetragenococcus halophilus in vitro. Antibiotic susceptibility of the transconjugants was host-dependent, and transconjugants maintained a lincomycin resistance phenotype in the absence of selective pressure over 60 generations.
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Affiliation(s)
- Jong-Hoon Lee
- Department of Food Science and Biotechnology, Kyonggi University, Suwon, 443–760, Republic of Korea
| | - Do-Won Jeong
- Department of Food Science and Biotechnology, Shinansan University, Ansan, 425–792, Republic of Korea
- * E-mail:
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Mishra D, Kato T, Inagaki H, Kosho T, Wakui K, Kido Y, Sakazume S, Taniguchi-Ikeda M, Morisada N, Iijima K, Fukushima Y, Emanuel BS, Kurahashi H. Breakpoint analysis of the recurrent constitutional t(8;22)(q24.13;q11.21) translocation. Mol Cytogenet 2014; 7:55. [PMID: 25478009 PMCID: PMC4255720 DOI: 10.1186/s13039-014-0055-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2014] [Accepted: 07/25/2014] [Indexed: 11/23/2022] Open
Abstract
Backgrounds The t(8;22)(q24.13;q11.2) has been identified as one of several recurrent
constitutional translocations mediated by palindromic AT-rich repeats (PATRRs).
Although the breakage on 22q11 utilizes the same PATRR as that of the more
prevalent constitutional t(11;22)(q23;q11.2), the breakpoint region on 8q24 has
not been elucidated in detail since the analysis of palindromic sequence is
technically challenging. Results In this study, the entire 8q24 breakpoint region has been resolved by next
generation sequencing. Eight polymorphic alleles were identified and compared with
the junction sequences of previous and two recently identified t(8;22) cases . All
of the breakpoints were found to be within the PATRRs on chromosomes 8 and 22
(PATRR8 and PATRR22), but the locations were different among cases at the level of
nucleotide resolution. The translocations were always found to arise on symmetric
PATRR8 alleles with breakpoints at the center of symmetry. The translocation
junction is often accompanied by symmetric deletions at the center of both PATRRs.
Rejoining occurs with minimal homology between the translocation partners.
Remarkably, comparison of der (8) to der(22) sequences shows identical breakpoint
junctions between them, which likely represent products of two independent events
on the basis of a classical model. Conclusions Our data suggest the hypothesis that interactions between the two PATRRs prior to
the translocation event might trigger illegitimate recombination resulting in the
recurrent palindrome-mediated translocation.
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Affiliation(s)
- Divya Mishra
- Division of Molecular Genetics, Institute for Comprehensive Medical Science, Fujita Health University, Toyoake 470-1192, Aichi, Japan
| | - Takema Kato
- Division of Molecular Genetics, Institute for Comprehensive Medical Science, Fujita Health University, Toyoake 470-1192, Aichi, Japan
| | - Hidehito Inagaki
- Division of Molecular Genetics, Institute for Comprehensive Medical Science, Fujita Health University, Toyoake 470-1192, Aichi, Japan
| | - Tomoki Kosho
- Department of Medical Genetics, Shinshu University School of Medicine, Matsumoto 390-8621, Nagano, Japan
| | - Keiko Wakui
- Department of Medical Genetics, Shinshu University School of Medicine, Matsumoto 390-8621, Nagano, Japan
| | - Yasuhiro Kido
- Department of Pediatrics, Dokkyo Medical University Koshigaya Hospital, Koshigaya 343-8555, Saitama, Japan
| | - Satoru Sakazume
- Department of Pediatrics, Dokkyo Medical University Koshigaya Hospital, Koshigaya 343-8555, Saitama, Japan
| | - Mariko Taniguchi-Ikeda
- Department of Pediatrics, Kobe University Graduate School of Medicine, Kobe 650-0017, Hyogo, Japan
| | - Naoya Morisada
- Department of Pediatrics, Kobe University Graduate School of Medicine, Kobe 650-0017, Hyogo, Japan
| | - Kazumoto Iijima
- Department of Pediatrics, Kobe University Graduate School of Medicine, Kobe 650-0017, Hyogo, Japan
| | - Yoshimitsu Fukushima
- Department of Medical Genetics, Shinshu University School of Medicine, Matsumoto 390-8621, Nagano, Japan
| | - Beverly S Emanuel
- Division of Human Genetics, The Children's Hospital of Philadelphia, Philadelphia 19104, PA, USA.,Department of Pediatrics, The Perelman School of Medicine of the University of Pennsylvania, Philadelphia 19104, PA, USA
| | - Hiroki Kurahashi
- Division of Molecular Genetics, Institute for Comprehensive Medical Science, Fujita Health University, Toyoake 470-1192, Aichi, Japan
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Hsiao YY, Fang WH, Lee CC, Chen YP, Yuan HS. Structural insights into DNA repair by RNase T--an exonuclease processing 3' end of structured DNA in repair pathways. PLoS Biol 2014; 12:e1001803. [PMID: 24594808 PMCID: PMC3942315 DOI: 10.1371/journal.pbio.1001803] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2013] [Accepted: 01/21/2014] [Indexed: 11/19/2022] Open
Abstract
DNA repair mechanisms are essential for preservation of genome integrity. However, it is not clear how DNA are selected and processed at broken ends by exonucleases during repair pathways. Here we show that the DnaQ-like exonuclease RNase T is critical for Escherichia coli resistance to various DNA-damaging agents and UV radiation. RNase T specifically trims the 3' end of structured DNA, including bulge, bubble, and Y-structured DNA, and it can work with Endonuclease V to restore the deaminated base in an inosine-containing heteroduplex DNA. Crystal structure analyses further reveal how RNase T recognizes the bulge DNA by inserting a phenylalanine into the bulge, and as a result the 3' end of blunt-end bulge DNA can be digested by RNase T. In contrast, the homodimeric RNase T interacts with the Y-structured DNA by a different binding mode via a single protomer so that the 3' overhang of the Y-structured DNA can be trimmed closely to the duplex region. Our data suggest that RNase T likely processes bulge and bubble DNA in the Endonuclease V-dependent DNA repair, whereas it processes Y-structured DNA in UV-induced and various other DNA repair pathways. This study thus provides mechanistic insights for RNase T and thousands of DnaQ-like exonucleases in DNA 3'-end processing.
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Affiliation(s)
- Yu-Yuan Hsiao
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan, Republic of China
- Department of Biological Science and Technology, National Chiao Tung University, Hsinchu, Taiwan, Republic of China
| | - Woei-Horng Fang
- Department of Clinical Laboratory Sciences and Medical Biotechnology, College of Medicine, National Taiwan University, Taipei, Taiwan, Republic of China
| | - Chia-Chia Lee
- Department of Clinical Laboratory Sciences and Medical Biotechnology, College of Medicine, National Taiwan University, Taipei, Taiwan, Republic of China
| | - Yi-Ping Chen
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan, Republic of China
| | - Hanna S. Yuan
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan, Republic of China
- Graduate Institute of Biochemistry and Molecular Biology, National Taiwan University, Taipei, Taiwan, Republic of China
- * E-mail:
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22
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Thirty-thousand-year-old distant relative of giant icosahedral DNA viruses with a pandoravirus morphology. Proc Natl Acad Sci U S A 2014; 111:4274-9. [PMID: 24591590 DOI: 10.1073/pnas.1320670111] [Citation(s) in RCA: 304] [Impact Index Per Article: 30.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The largest known DNA viruses infect Acanthamoeba and belong to two markedly different families. The Megaviridae exhibit pseudo-icosahedral virions up to 0.7 μm in diameter and adenine-thymine (AT)-rich genomes of up to 1.25 Mb encoding a thousand proteins. Like their Mimivirus prototype discovered 10 y ago, they entirely replicate within cytoplasmic virion factories. In contrast, the recently discovered Pandoraviruses exhibit larger amphora-shaped virions 1 μm in length and guanine-cytosine-rich genomes up to 2.8 Mb long encoding up to 2,500 proteins. Their replication involves the host nucleus. Whereas the Megaviridae share some general features with the previously described icosahedral large DNA viruses, the Pandoraviruses appear unrelated to them. Here we report the discovery of a third type of giant virus combining an even larger pandoravirus-like particle 1.5 μm in length with a surprisingly smaller 600 kb AT-rich genome, a gene content more similar to Iridoviruses and Marseillevirus, and a fully cytoplasmic replication reminiscent of the Megaviridae. This suggests that pandoravirus-like particles may be associated with a variety of virus families more diverse than previously envisioned. This giant virus, named Pithovirus sibericum, was isolated from a >30,000-y-old radiocarbon-dated sample when we initiated a survey of the virome of Siberian permafrost. The revival of such an ancestral amoeba-infecting virus used as a safe indicator of the possible presence of pathogenic DNA viruses, suggests that the thawing of permafrost either from global warming or industrial exploitation of circumpolar regions might not be exempt from future threats to human or animal health.
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Abstract
Bacterial genomes are remarkably stable from one generation to the next but are plastic on an evolutionary time scale, substantially shaped by horizontal gene transfer, genome rearrangement, and the activities of mobile DNA elements. This implies the existence of a delicate balance between the maintenance of genome stability and the tolerance of genome instability. In this review, we describe the specialized genetic elements and the endogenous processes that contribute to genome instability. We then discuss the consequences of genome instability at the physiological level, where cells have harnessed instability to mediate phase and antigenic variation, and at the evolutionary level, where horizontal gene transfer has played an important role. Indeed, this ability to share DNA sequences has played a major part in the evolution of life on Earth. The evolutionary plasticity of bacterial genomes, coupled with the vast numbers of bacteria on the planet, substantially limits our ability to control disease.
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24
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Recombination and annealing pathways compete for substrates in making rrn duplications in Salmonella enterica. Genetics 2013; 196:119-35. [PMID: 24214339 DOI: 10.1534/genetics.113.158519] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Tandem genetic duplications arise frequently between the seven directly repeated 5.5-kb rrn loci that encode ribosomal RNAs in Salmonella enterica. The closest rrn genes, rrnB and rrnE, flank a 40-kb region that includes the purHD operon. Duplications of purHD arise by exchanges between rrn loci and form at a high rate (10(-3)/cell/division) that remains high in strains blocked for early steps in recombination (recA, recB, and/or recF), but drops 30-fold in mutants blocked for later Holliday junction resolution (ruvC recG). The duplication defect of a ruvC recG mutant was fully corrected by an added mutation in any one of the recA, recB, or recF genes. To explain these results, we propose that early recombination defects activate an alternative single-strand annealing pathway for duplication formation. In wild-type cells, rrn duplications form primarily by the action of RecFORA on single-strand gaps. Double-strand breaks cannot initiate rrn duplications because rrn loci lack Chi sites, which are essential for recombination between two separated rrn sequences. A recA or recF mutation allows unrepaired gaps to accumulate such that different rrn loci can provide single-strand rrn sequences that lack the RecA coating that normally inhibits annealing. A recB mutation activates annealing by allowing double-strand ends within rrn to avoid digestion by RecBCD and provide a new source of rrn ends for use in annealing. The equivalent high rates of rrn duplication by recombination and annealing pathways may reflect a limiting economy of gaps and breaks arising in heavily transcribed, palindrome-rich rrn sequences.
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25
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Johnson S, Chen YJ, Phillips R. Poly(dA:dT)-rich DNAs are highly flexible in the context of DNA looping. PLoS One 2013; 8:e75799. [PMID: 24146776 PMCID: PMC3795714 DOI: 10.1371/journal.pone.0075799] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2013] [Accepted: 08/19/2013] [Indexed: 01/31/2023] Open
Abstract
Large-scale DNA deformation is ubiquitous in transcriptional regulation in prokaryotes and eukaryotes alike. Though much is known about how transcription factors and constellations of binding sites dictate where and how gene regulation will occur, less is known about the role played by the intervening DNA. In this work we explore the effect of sequence flexibility on transcription factor-mediated DNA looping, by drawing on sequences identified in nucleosome formation and ligase-mediated cyclization assays as being especially favorable for or resistant to large deformations. We examine a poly(dA:dT)-rich, nucleosome-repelling sequence that is often thought to belong to a class of highly inflexible DNAs; two strong nucleosome positioning sequences that share a set of particular sequence features common to nucleosome-preferring DNAs; and a CG-rich sequence representative of high G+C-content genomic regions that correlate with high nucleosome occupancy in vivo. To measure the flexibility of these sequences in the context of DNA looping, we combine the in vitro single-molecule tethered particle motion assay, a canonical looping protein, and a statistical mechanical model that allows us to quantitatively relate the looping probability to the looping free energy. We show that, in contrast to the case of nucleosome occupancy, G+C content does not positively correlate with looping probability, and that despite sharing sequence features that are thought to determine nucleosome affinity, the two strong nucleosome positioning sequences behave markedly dissimilarly in the context of looping. Most surprisingly, the poly(dA:dT)-rich DNA that is often characterized as highly inflexible in fact exhibits one of the highest propensities for looping that we have measured. These results argue for a need to revisit our understanding of the mechanical properties of DNA in a way that will provide a basis for understanding DNA deformation over the entire range of biologically relevant scenarios that are impacted by DNA deformability.
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Affiliation(s)
- Stephanie Johnson
- Department of Biochemistry and Molecular Biophysics, California Institute of Technology, Pasadena, California, United States of America
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California, United States of America
| | - Yi-Ju Chen
- Department of Physics, California Institute of Technology, Pasadena, California, United States of America
| | - Rob Phillips
- Departments of Applied Physics and Biology, California Institute of Technology, Pasadena, California, United States of America
- * E-mail:
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26
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Repar J, Briški N, Buljubašić M, Zahradka K, Zahradka D. Exonuclease VII is involved in "reckless" DNA degradation in UV-irradiated Escherichia coli. Mutat Res 2012; 750:96-104. [PMID: 23123979 DOI: 10.1016/j.mrgentox.2012.10.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2012] [Revised: 09/17/2012] [Accepted: 10/10/2012] [Indexed: 01/06/2023]
Abstract
The recA mutants of Escherichia coli exhibit an abnormal DNA degradation that starts at sites of double-strand DNA breaks (DSBs), and is mediated by RecBCD exonuclease (ExoV). This "reckless" DNA degradation occurs spontaneously in exponentially growing recA cells, and is stimulated by DNA-damaging agents. We have previously found that the xonA and sbcD mutations, which inactivate exonuclease I (ExoI) and SbcCD nuclease, respectively, markedly suppress "reckless" DNA degradation in UV-irradiated recA cells. In the present work, we show that inactivation of exonuclease VII (ExoVII) by an xseA mutation contributes to attenuation of DNA degradation in UV-irradiated recA mutants. The xseA mutation itself has only a weak effect, however, it acts synergistically with the xonA or sbcD mutations in suppressing "reckless" DNA degradation. The quadruple xseA xonA sbcD recA mutants show no sign of DNA degradation during post-irradiation incubation, suggesting that ExoVII, together with ExoI and SbcCD, plays a crucial role in regulating RecBCD-catalyzed chromosome degradation. We propose that these nucleases act on DSBs to create blunt DNA ends, the preferred substrates for the RecBCD enzyme. In addition, our results show that in UV-irradiated recF recA(+) cells, the xseA, xonA, and sbcD mutations do not affect RecBCD-mediated DNA repair, suggesting that ExoVII, ExoI and SbcCD nucleases are not essential for the initial targeting of RecBCD to DSBs. It is possible that the DNA-blunting activity provided by ExoVII, ExoI and SbcCD is required for an exchange of RecBCD molecules on dsDNA ends during ongoing "reckless" DNA degradation.
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Affiliation(s)
- Jelena Repar
- Division of Molecular Biology, Ruđer Bošković Institute, Bijenička, Zagreb, Croatia
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27
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Reams AB, Kofoid E, Kugelberg E, Roth JR. Multiple pathways of duplication formation with and without recombination (RecA) in Salmonella enterica. Genetics 2012; 192:397-415. [PMID: 22865732 PMCID: PMC3454872 DOI: 10.1534/genetics.112.142570] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2012] [Accepted: 07/24/2012] [Indexed: 12/11/2022] Open
Abstract
Duplications are often attributed to "unequal recombination" between separated, directly repeated sequence elements (>100 bp), events that leave a recombinant element at the duplication junction. However, in the bacterial chromosome, duplications form at high rates (10(-3)-10(-5)/cell/division) even without recombination (RecA). Here we describe 1800 spontaneous lac duplications trapped nonselectively on the low-copy F'(128) plasmid, where lac is flanked by direct repeats of the transposable element IS3 (1258 bp) and by numerous quasipalindromic REP elements (30 bp). Duplications form at a high rate (10(-4)/cell/division) that is reduced only about 11-fold in the absence of RecA. With and without RecA, most duplications arise by recombination between IS3 elements (97%). Formation of these duplications is stimulated by IS3 transposase (Tnp) and plasmid transfer functions (TraI). Three duplication pathways are proposed. First, plasmid dimers form at a high rate stimulated by RecA and are then modified by deletions between IS3 elements (resolution) that leave a monomeric plasmid with an IS3-flanked lac duplication. Second, without RecA, duplications occur by single-strand annealing of DNA ends generated in different sister chromosomes after transposase nicks DNA near participating IS3 elements. The absence of RecA may stimulate annealing by allowing chromosome breaks to persist. Third, a minority of lac duplications (3%) have short (0-36 bp) junction sequences (SJ), some of which are located within REP elements. These duplication types form without RecA, Tnp, or Tra by a pathway in which the palindromic junctions of a tandem inversion duplication (TID) may stimulate deletions that leave the final duplication.
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Affiliation(s)
- Andrew B. Reams
- Department of Microbiology, University of California, Davis, California 95616
| | - Eric Kofoid
- Department of Microbiology, University of California, Davis, California 95616
| | - Elisabeth Kugelberg
- Department of Microbiology, University of California, Davis, California 95616
| | - John R. Roth
- Department of Microbiology, University of California, Davis, California 95616
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Damas J, Carneiro J, Gonçalves J, Stewart JB, Samuels DC, Amorim A, Pereira F. Mitochondrial DNA deletions are associated with non-B DNA conformations. Nucleic Acids Res 2012; 40:7606-21. [PMID: 22661583 PMCID: PMC3439893 DOI: 10.1093/nar/gks500] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Mitochondrial DNA (mtDNA) deletions are a primary cause of mitochondrial disease and are believed to contribute to the aging process and to various neurodegenerative diseases. Despite strong observational and experimental evidence, the molecular basis of the deletion process remains obscure. In this study, we test the hypothesis that the primary cause of mtDNA vulnerability to breakage resides in the formation of non-B DNA conformations, namely hairpin, cruciform and cloverleaf-like elements. Using the largest database of human mtDNA deletions built thus far (753 different cases), we show that site-specific breakage hotspots exist in the mtDNA. Furthermore, we discover that the most frequent deletion breakpoints occur within or near predicted structures, a result that is supported by data from transgenic mice with mitochondrial disease. There is also a significant association between the folding energy of an mtDNA region and the number of breakpoints that it harbours. In particular, two clusters of hairpins (near the D-loop 3′-terminus and the L-strand origin of replication) are hotspots for mtDNA breakage. Consistent with our hypothesis, the highest number of 5′- and 3′-breakpoints per base is found in the highly structured tRNA genes. Overall, the data presented in this study suggest that non-B DNA conformations are a key element of the mtDNA deletion process.
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Affiliation(s)
- Joana Damas
- Institute of Molecular Pathology and Immunology, University of Porto (IPATIMUP), Rua Dr Roberto Frias s/n, 4200-465 Porto, Portugal
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Abstract
In recent years, our understanding of the functioning of ABC (ATP-binding cassette) systems has been boosted by the combination of biochemical and structural approaches. However, the origin and the distribution of ABC proteins among living organisms are difficult to understand in a phylogenetic perspective, because it is hard to discriminate orthology and paralogy, due to the existence of horizontal gene transfer. In this chapter, I present an update of the classification of ABC systems and discuss a hypothetical scenario of their evolution. The hypothetical presence of ABC ATPases in the last common ancestor of modern organisms is discussed, as well as the additional possibility that ABC systems might have been transmitted to eukaryotes, after the two endosymbiosis events that led to the constitution of eukaryotic organelles. I update the functional information of selected ABC systems and introduce new families of ABC proteins that have been included recently into this vast superfamily, thanks to the availability of high-resolution three-dimensional structures.
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Kurahashi H, Inagaki H, Ohye T, Kogo H, Tsutsumi M, Kato T, Tong M, Emanuel BS. The constitutional t(11;22): implications for a novel mechanism responsible for gross chromosomal rearrangements. Clin Genet 2011; 78:299-309. [PMID: 20507342 DOI: 10.1111/j.1399-0004.2010.01445.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The constitutional t(11;22)(q23;q11) is the most common recurrent non-Robertsonian translocation in humans. The breakpoint sequences of both chromosomes are characterized by several hundred base pairs of palindromic AT-rich repeats (PATRRs). Similar PATRRs have also been identified at the breakpoints of other nonrecurrent translocations, suggesting that PATRR-mediated chromosomal translocation represents one of the universal pathways for gross chromosomal rearrangement in the human genome. We propose that PATRRs have the potential to form cruciform structures through intrastrand-base pairing in single-stranded DNA, creating a source of genomic instability and leading to translocations. Indeed, de novo examples of the t(11;22) are detected at a high frequency in sperm from normal healthy males. This review synthesizes recent data illustrating a novel paradigm for an apparent spermatogenesis-specific translocation mechanism. This observation has important implications pertaining to the predominantly paternal origin of de novo gross chromosomal rearrangements in humans.
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Affiliation(s)
- H Kurahashi
- Division of Molecular Genetics, Institute for Comprehensive Medical Science, Fujita Health University, Toyoake, Aichi, Japan.
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31
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Gupta R, Barkan D, Redelman-Sidi G, Shuman S, Glickman MS. Mycobacteria exploit three genetically distinct DNA double-strand break repair pathways. Mol Microbiol 2010; 79:316-30. [PMID: 21219454 DOI: 10.1111/j.1365-2958.2010.07463.x] [Citation(s) in RCA: 85] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Bacterial pathogens rely on their DNA repair pathways to resist genomic damage inflicted by the host. DNA double-strand breaks (DSBs) are especially threatening to bacterial viability. DSB repair by homologous recombination (HR) requires nucleases that resect DSB ends and a strand exchange protein that facilitates homology search. RecBCD and RecA perform these functions in Escherichia coli and constitute the major pathway of error-free DSB repair. Mycobacteria, including the human pathogen M. tuberculosis, elaborate an additional error-prone pathway of DSB repair via non-homologous end-joining (NHEJ) catalysed by Ku and DNA ligase D (LigD). Little is known about the relative contributions of HR and NHEJ to mycobacterial chromosome repair, the factors that dictate pathway choice, or the existence of additional DSB repair pathways. Here we demonstrate that Mycobacterium smegmatis has three DSB repair pathway options: HR, NHEJ and a novel mechanism of single-strand annealing (SSA). Inactivation of NHEJ or SSA is compensated by elevated HR. We find that mycobacterial RecBCD does not participate in HR or confer resistance to ionizing radiation (IR), but is required for the RecA-independent SSA pathway. In contrast, the mycobacterial helicase-nuclease AdnAB participates in the RecA-dependent HR pathway, and is a major determinant of resistance to IR and oxidative DNA damage. These findings reveal distinctive features of mycobacterial DSB repair, most notably the dedication of the RecBCD and AdnAB helicase-nuclease machines to distinct repair pathways.
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Affiliation(s)
- Richa Gupta
- Immunology Program Molecular Biology Program, Sloan-Kettering Institute, New York, NY 10065, USA
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32
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Tong M, Kato T, Yamada K, Inagaki H, Kogo H, Ohye T, Tsutsumi M, Wang J, Emanuel BS, Kurahashi H. Polymorphisms of the 22q11.2 breakpoint region influence the frequency of de novo constitutional t(11;22)s in sperm. Hum Mol Genet 2010; 19:2630-7. [PMID: 20392709 DOI: 10.1093/hmg/ddq150] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The constitutional t(11;22) is the most frequent recurrent non-Robertsonian translocation in humans, the breakpoints of which are located within palindromic AT-rich repeats on 11q23 and 22q11 (PATRR11 and PATRR22). Genetic variation of the PATRR11 was found to affect de novo t(11;22) translocation frequency in sperm derived from normal healthy males, suggesting the hypothesis that polymorphisms of the PATRR22 might also influence the translocation frequency. Although the complicated structure of the PATRR22 locus prevented determining the genotype of the PATRR22 in each individual, genotyping of flanking markers as well as identification of rare variants allowed us to demonstrate an association between the PATRR22 allele type and the translocation frequency. We found that size and symmetry of the PATRR22 affect the de novo translocation frequency, which is lower for the shorter or more asymmetric versions. These data lend support to our hypothesis that the PATRRs form secondary structures in the nucleus that induce genomic instability leading to the recurrent translocation.
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Affiliation(s)
- Maoqing Tong
- Institute for Comprehensive Medical Science, Fujita Health University, Aichi, Japan
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33
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Andreoni F, Darmon E, Poon WCK, Leach DRF. Overexpression of the single-stranded DNA-binding protein (SSB) stabilises CAG*CTG triplet repeats in an orientation dependent manner. FEBS Lett 2010; 584:153-8. [PMID: 19925793 DOI: 10.1016/j.febslet.2009.11.042] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2009] [Accepted: 11/09/2009] [Indexed: 11/18/2022]
Abstract
The stability and deletion-size-distribution profiles of leading strand (CAG)(75) and (CTG)(137) trinucleotide repeat arrays inserted in the Escherichia coli chromosome were investigated upon overexpression of the single-stranded DNA-binding protein (SSB) and in mutant strains deficient for the SbcCD (Rad51/Mre11) nuclease. SSB overexpression increases the stability of the (CAG)(75) repeat array and leads to a loss of the bias towards large deletions for the same array. Furthermore, the absence of SbcCD leads to a reduction in the number of large deletions in strains containing the (CTG)(137) repeat array.
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Affiliation(s)
- Federica Andreoni
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, UK
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34
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Noothi SK, Minda R, Rao BJ. MutS and UvrD Proteins Stimulate Exonuclease Action: Insights into Exonuclease-Mediated Strand Repair. Biochemistry 2009; 48:7787-93. [DOI: 10.1021/bi8020313] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Sunil K. Noothi
- Department of Biological Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India
| | - Renu Minda
- Department of Biological Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India
| | - Basuthkar J. Rao
- Department of Biological Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India
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Kurahashi H, Inagaki H, Kato T, Hosoba E, Kogo H, Ohye T, Tsutsumi M, Bolor H, Tong M, Emanuel BS. Impaired DNA replication prompts deletions within palindromic sequences, but does not induce translocations in human cells. Hum Mol Genet 2009; 18:3397-406. [PMID: 19520744 DOI: 10.1093/hmg/ddp279] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Palindromic regions are unstable and susceptible to deletion in prokaryotes and eukaryotes possibly due to stalled or slow replication. In the human genome, they also appear to become partially or completely deleted, while two palindromic AT-rich repeats (PATRR) contribute to known recurrent constitutional translocations. To explore the mechanism that causes the development of palindrome instabilities in humans, we compared the incidence of de novo translocations and deletions at PATRRs in human cells. Using a highly sensitive PCR assay that can detect single molecules, de novo deletions were detected neither in human somatic cells nor in sperm. However, deletions were detected at low frequency in cultured cell lines. Inhibition of DNA replication by administration of siRNA against the DNA polymerase alpha 1 (POLA1) gene or introduction of POLA inhibitors increased the frequency. This is in contrast to PATRR-mediated translocations that were never detected in similar conditions but were observed frequently in human sperm samples. Further deletions were found to take place during both leading- and lagging-strand synthesis. Our data suggest that stalled or slow replication induces deletions within PATRRs, but that other mechanisms might contribute to PATRR-mediated recurrent translocations in humans.
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Affiliation(s)
- Hiroki Kurahashi
- Division of Molecular Genetics, Fujita Health University, Toyoake, Aichi, Japan.
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36
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Sharples GJ. For absent friends: life without recombination in mutualistic gamma-proteobacteria. Trends Microbiol 2009; 17:233-42. [PMID: 19464894 DOI: 10.1016/j.tim.2009.03.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2008] [Revised: 03/23/2009] [Accepted: 03/24/2009] [Indexed: 12/01/2022]
Abstract
Almost all cellular organisms employ RecA orthologues to guide the strand invasion reactions necessary for DNA recombination and repair. One of the few exceptions to this orthodoxy is a group of gamma-proteobacteria flourishing in obligate intracellular symbiosis with insects and deep-sea clams. The apparent inability of these bacteria to commence the recombinational exchange process seems to confer genetic stability by preventing any further rearrangements or lateral transfer events. Although debate has centred on the absence of selected recombination functions and their impact on a fixed genomic architecture, no explanation has been offered for how bacteria survive the loss of such an integral DNA repair system. This question is addressed here by speculating on how the current repertoire of recombinases in symbiotic bacteria could enable recovery from potentially lethal injuries to the DNA template. Depending on which functions remain, several different options are plausible. The possibility that specific defects in recombination encourage radical genome erosion in mutualistic endosymbionts and other intracellular bacteria is discussed.
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Affiliation(s)
- Gary J Sharples
- School of Biological and Biomedical Sciences, University of Durham, Department of Chemistry, South Road, Durham DH1 3LE, UK.
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37
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Persky NS, Lovett ST. Mechanisms of Recombination: Lessons fromE. coli. Crit Rev Biochem Mol Biol 2009; 43:347-70. [DOI: 10.1080/10409230802485358] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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38
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Mariscotti JF, García-Del Portillo F. Instability of the Salmonella RcsCDB signalling system in the absence of the attenuator IgaA. MICROBIOLOGY-SGM 2008; 154:1372-1383. [PMID: 18451046 DOI: 10.1099/mic.0.2007/015891-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
IgaA is a Salmonella enterica membrane protein that attenuates the response of the RcsCDB signalling system to envelope stress. This protein is essential unless the RcsCDB system is inactivated, suggesting that IgaA may constantly adjust the magnitude of the response. Such a functional link is also supported by the concurrence of the igaA and rcsD-rcsB-rcsC loci in genomes of enteric bacteria and the selection of spontaneous mutations in the RcsCDB system following IgaA deprivation. However, the exact nature of the spontaneous mutations rendering IgaA dispensable remains undefined. In this work, we examined how the transduction of an igaA null allele affects the status of the RcsCDB system. Loss of RcsCDB response was registered in approximately 90 % of the IgaA-defective clones, which failed to produce the capsule material positively regulated by this system. About half of these non-mucoid clones suppressed the loss of IgaA with large deletions encompassing variable regions of the rcsD-rcsB-rcsC locus. Unexpectedly, mucoid transductants were also reproducibly obtained and indicated the capacity of S. enterica to retain a functional RcsCDB system in the absence of IgaA. Decreased levels of either RcsC or RcsD were shown in 'mucoid' clones lacking IgaA and displaying low responsiveness to stimuli. Taken together, these data demonstrate that the stability and responsiveness of the RcsCDB system relies on its attenuator IgaA. The type of suppressions found also support a model with IgaA controlling the level of signal flowing through RcsC and RcsD.
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Affiliation(s)
- Javier F Mariscotti
- Departamento de Biotecnología Microbiana, Centro Nacional de Biotecnología-Consejo Superior de Investigaciones Científicas (CSIC), Darwin 3, 28049 Madrid, Spain
| | - Francisco García-Del Portillo
- Departamento de Biotecnología Microbiana, Centro Nacional de Biotecnología-Consejo Superior de Investigaciones Científicas (CSIC), Darwin 3, 28049 Madrid, Spain
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39
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Lu L, Jia H, Dröge P, Li J. The human genome-wide distribution of DNA palindromes. Funct Integr Genomics 2007; 7:221-7. [PMID: 17340149 DOI: 10.1007/s10142-007-0047-6] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2006] [Revised: 02/05/2007] [Accepted: 02/19/2007] [Indexed: 10/23/2022]
Abstract
In this work, we performed a systematic study of perfect and nonspacer palindromes present in human genomic DNA, and we investigated palindrome distribution over the entire human genome and over the functional regions such as the exon, intron, intergenic, and upstream regions (2,000 bp upstream from translational start site). We found that 24 palindrome-abundant intervals are mostly located on G-bands, which condense early, replicate late, and are relatively A+T rich. In general, palindromes are overrepresented in introns but underrepresented in exons. Upstream region has enriched palindrome distribution, where palindromes can serve as transcription factor binding sites. We created a Human DNA Palindrome Database (HPALDB) which is accessible at http://vhp.ntu.edu.sg/hpaldb . It contains 12,556,994 entries covering all palindromes in the human genome longer than 6 bp. Queries can be performed in different ways. Each entry in the database is linked to its location on NCBI's human chromosome Map Viewer.
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Affiliation(s)
- Le Lu
- Division of Structural and Computational Biology, School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore 637551, Singapore
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40
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Zahra R, Blackwood JK, Sales J, Leach DRF. Proofreading and secondary structure processing determine the orientation dependence of CAG x CTG trinucleotide repeat instability in Escherichia coli. Genetics 2007; 176:27-41. [PMID: 17339223 PMCID: PMC1893049 DOI: 10.1534/genetics.106.069724] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Expanded CAG x CTG trinucleotide repeat tracts are associated with several human inherited diseases, including Huntington's disease, myotonic dystrophy, and spinocerebellar ataxias. Here we describe a new model system to investigate repeat instability in the Escherichia coli chromosome. Using this system, we reveal patterns of deletion instability consistent with secondary structure formation in vivo and address the molecular basis of orientation-dependent instability. We demonstrate that the orientation dependence of CAG x CTG trinucleotide repeat deletion is determined by the proofreading subunit of DNA polymerase III (DnaQ) in the presence of the hairpin nuclease SbcCD (Rad50/Mre11). Our results suggest that, although initiation of slippage can occur independently of CAG x CTG orientation, the folding of the intermediate affects its processing and this results in orientation dependence. We propose that proofreading is inefficient on the CTG-containing strand because of its ability to misfold and that SbcCD contributes to processing in a manner that is dependent on proofreading and repeat tract orientation. Furthermore, we demonstrate that transcription and recombination do not influence instability in this system.
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Affiliation(s)
- Rabaab Zahra
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom
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41
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Kogo H, Inagaki H, Ohye T, Kato T, Emanuel BS, Kurahashi H. Cruciform extrusion propensity of human translocation-mediating palindromic AT-rich repeats. Nucleic Acids Res 2007; 35:1198-208. [PMID: 17264116 PMCID: PMC1851657 DOI: 10.1093/nar/gkm036] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
There is an emerging consensus that secondary structures of DNA have the potential for genomic instability. Palindromic AT-rich repeats (PATRRs) are a characteristic sequence identified at each breakpoint of the recurrent constitutional t(11;22) and t(17;22) translocations in humans, named PATRR22 (∼600 bp), PATRR11 (∼450 bp) and PATRR17 (∼190 bp). The secondary structure-forming propensity in vitro and the instability in vivo have been experimentally evaluated for various PATRRs that differ regarding their size and symmetry. At physiological ionic strength, a cruciform structure is most frequently observed for the symmetric PATRR22, less often for the symmetric PATRR11, but not for the other PATRRs. In wild-type E. coli, only these two PATRRs undergo extensive instability, consistent with the relatively high incidence of the t(11;22) in humans. The resultant deletions are putatively mediated by central cleavage by the structure-specific endonuclease SbcCD, indicating the possibility of a cruciform conformation in vivo. Insertion of a short spacer at the centre of the PATRR22 greatly reduces both its cruciform extrusion in vitro and instability in vivo. Taken together, cruciform extrusion propensity depends on the length and central symmetry of the PATRR, and is likely to determine the instability that leads to recurrent translocations in humans.
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MESH Headings
- AT Rich Sequence
- Chromosomes, Human, Pair 11
- Chromosomes, Human, Pair 17
- Chromosomes, Human, Pair 22
- DNA, Cruciform/chemistry
- Deoxyribonucleases/metabolism
- Electrophoretic Mobility Shift Assay
- Escherichia coli/genetics
- Escherichia coli Proteins/metabolism
- Genomic Instability
- Humans
- Nucleic Acid Conformation
- Repetitive Sequences, Nucleic Acid
- Sequence Analysis, DNA
- Sequence Deletion
- Translocation, Genetic
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Affiliation(s)
- Hiroshi Kogo
- Division of Molecular Genetics, Institute for Comprehensive Medical Science, Fujita Health University, Toyoake, Aichi 470-1192, Japan, 21st Century COE Program, Development Center for Targeted and Minimally Invasive Diagnosis and Treatment, Fujita Health University, Toyoake, Aichi 470-1192, Japan, Division of Human Genetics, The Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA and Department of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
| | - Hidehito Inagaki
- Division of Molecular Genetics, Institute for Comprehensive Medical Science, Fujita Health University, Toyoake, Aichi 470-1192, Japan, 21st Century COE Program, Development Center for Targeted and Minimally Invasive Diagnosis and Treatment, Fujita Health University, Toyoake, Aichi 470-1192, Japan, Division of Human Genetics, The Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA and Department of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
| | - Tamae Ohye
- Division of Molecular Genetics, Institute for Comprehensive Medical Science, Fujita Health University, Toyoake, Aichi 470-1192, Japan, 21st Century COE Program, Development Center for Targeted and Minimally Invasive Diagnosis and Treatment, Fujita Health University, Toyoake, Aichi 470-1192, Japan, Division of Human Genetics, The Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA and Department of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
| | - Takema Kato
- Division of Molecular Genetics, Institute for Comprehensive Medical Science, Fujita Health University, Toyoake, Aichi 470-1192, Japan, 21st Century COE Program, Development Center for Targeted and Minimally Invasive Diagnosis and Treatment, Fujita Health University, Toyoake, Aichi 470-1192, Japan, Division of Human Genetics, The Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA and Department of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
| | - Beverly S. Emanuel
- Division of Molecular Genetics, Institute for Comprehensive Medical Science, Fujita Health University, Toyoake, Aichi 470-1192, Japan, 21st Century COE Program, Development Center for Targeted and Minimally Invasive Diagnosis and Treatment, Fujita Health University, Toyoake, Aichi 470-1192, Japan, Division of Human Genetics, The Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA and Department of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
| | - Hiroki Kurahashi
- Division of Molecular Genetics, Institute for Comprehensive Medical Science, Fujita Health University, Toyoake, Aichi 470-1192, Japan, 21st Century COE Program, Development Center for Targeted and Minimally Invasive Diagnosis and Treatment, Fujita Health University, Toyoake, Aichi 470-1192, Japan, Division of Human Genetics, The Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA and Department of Pediatrics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
- *To whom correspondence should be addressed. Tel: +81 562 939391; Fax: +81 562 938831;
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42
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Gómez-Valero L, Silva FJ, Christophe Simon J, Latorre A. Genome reduction of the aphid endosymbiont Buchnera aphidicola in a recent evolutionary time scale. Gene 2006; 389:87-95. [PMID: 17098378 DOI: 10.1016/j.gene.2006.10.001] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2006] [Revised: 09/27/2006] [Accepted: 10/01/2006] [Indexed: 10/24/2022]
Abstract
Genome reduction, a typical feature of symbiotic bacteria, was analyzed in the last stages of evolution of Buchnera aphidicola, the primary aphid endosymbiont, in two neutrally evolving regions: the pseudogene cmk and an intergenic region. These two regions were examined in endosymbionts from several lineages of their aphid host Rhopalosiphum padi, and different species of the same genus, whose divergence times ranged from 0.62 to 19.51 million years. Estimates of nucleotide substitution rates were between 4.3 and 6.7x10(-9) substitution/site/year, with G or C nucleotides being substituted around four times more frequently than A or T. Two different types of indel events were detected, of which many were small (1-10 nt) but one was large (about 200 nucleotides). With respect to the large one and considering the proportion and size of the deletions and insertions, the reduction rate was 1.3x10(-8) lost nucleotides/site/year. We propose a stepwise scenario for the last stages of evolution in B. aphidicola: together with a very slow and gradual degradation, considerable indels would punctually emerge. The only restriction to large deletion fixation is that the lost fragment does not contain essential genes.
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Affiliation(s)
- Laura Gómez-Valero
- Institut Cavanilles de Biodiversitat i Biologia Evolutiva and Departament de Genètica, Universitat de València, Apartat 22085, 46071 Valencia, Spain
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43
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Kurahashi H, Inagaki H, Ohye T, Kogo H, Kato T, Emanuel BS. Palindrome-mediated chromosomal translocations in humans. DNA Repair (Amst) 2006; 5:1136-45. [PMID: 16829213 PMCID: PMC2824556 DOI: 10.1016/j.dnarep.2006.05.035] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Recently, it has emerged that palindrome-mediated genomic instability contributes to a diverse group of genomic rearrangements including translocations, deletions, and amplifications. One of the best studied examples is the recurrent t(11;22) constitutional translocation in humans that has been well documented to be mediated by palindromic AT-rich repeats (PATRRs) on chromosomes 11q23 and 22q11. De novo examples of the translocation are detected at a high frequency in sperm samples from normal healthy males, but not in lymphoblasts or fibroblasts. Cloned breakpoint sequences preferentially form a cruciform configuration in vitro. Analysis of the junction fragments implicates frequent double-strand-breaks (DSBs) at the center of both palindromic regions, followed by repair through the non-homologous end joining (NHEJ) pathway. We propose that the PATRR adopts a cruciform structure in male meiotic cells, creating genomic instability that leads to the recurrent translocation.
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Affiliation(s)
- Hiroki Kurahashi
- Division of Molecular Genetics, Institute for Comprehensive Medical Science, Fujita Health University, Toyoake, Aichi 470-1192, Japan.
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44
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Abstract
DNA palindromes are a source of instability in eukaryotic genomes but remain under-investigated because they are difficult to study. Nonetheless, progress in the last year or so has begun to form a coherent picture of how DNA palindromes cause damage in eukaryotes and how this damage is opposed by cellular mechanisms. In yeast, the features of double strand DNA interruptions that appear at palindromic sites in vivo suggest that a resolvase-type activity creates the fractures by attacking a palindrome after it extrudes into a cruciform structure. Induction of DNA breaks in this fashion could be deterred through a Center-Break palindrome revision process as investigated in detail in mice. The MRX/MRN likely plays a pivotal role in prevention of palindrome-induced genome damage in eukaryotes.
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Affiliation(s)
- Susanna M Lewis
- Graduate Department of Molecular and Medical Genetics, University of Toronto, Ont., Canada.
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45
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Bacolla A, Wojciechowska M, Kosmider B, Larson JE, Wells RD. The involvement of non-B DNA structures in gross chromosomal rearrangements. DNA Repair (Amst) 2006; 5:1161-70. [PMID: 16807140 DOI: 10.1016/j.dnarep.2006.05.032] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Non-B DNA conformations adopted by certain types of DNA sequences promote genetic instabilities, especially gross rearrangements including translocations. We conclude the following: (a) slipped (hairpin) structures, cruciforms, triplexes, tetraplexes and i-motifs, and left-handed Z-DNA are formed in chromosomes and elicit profound genetic consequences via recombination-repair, (b) repeating sequences, probably in their non-B conformations, cause gross genomic rearrangements (translocations, deletions, insertions, inversions, and duplications), and (c) these rearrangements are the genetic basis for numerous human diseases including polycystic kidney disease, adrenoleukodystrophy, follicular lymphomas, and spermatogenic failure.
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Affiliation(s)
- Albino Bacolla
- Institute of Biosciences and Technology, Center for Genome Research, The Texas A&M University System Health Science Center, Texas Medical Center, 2121 West Holcombe Blvd., Houston, TX 77030, USA.
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46
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Goldfless SJ, Morag AS, Belisle KA, Sutera VA, Lovett ST. DNA repeat rearrangements mediated by DnaK-dependent replication fork repair. Mol Cell 2006; 21:595-604. [PMID: 16507358 DOI: 10.1016/j.molcel.2006.01.025] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2005] [Revised: 01/11/2006] [Accepted: 01/17/2006] [Indexed: 10/25/2022]
Abstract
We propose that rearrangements between short tandem repeated sequences occur by errors made during a replication fork repair pathway involving a replication template switch. We provide evidence here that the DnaK chaperone of E. coli controls this template switch repair process. Mutants in dnaK are sensitive to replication fork damage and exhibit high expression of the SOS response, indicative of repair deficiency. Deletion and expansion of tandem repeats that occur by replication misalignment ("slippage") are also DnaK dependent. Because mutations in dnaX encoding the gamma and tau subunits of DNA polymerase III mimic dnaK phenotypes and are genetically epistatic, we propose that the DnaKJ chaperone remodels the replisome to facilitate repair. The fork remains largely intact because PriA or PriC restart proteins are not required. We also suggest that the poorly defined RAD6-RAD18-RAD5 mechanism of postreplication repair in eukaryotes occurs by an analogous mechanism to the DnaK template-switch pathway in prokaryotes.
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Affiliation(s)
- Stephen J Goldfless
- Department of Biology and Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachusetts 02454, USA
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47
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Abstract
Repetitive DNA sequences are abundant in eukaryotic genomes, and many of these sequences have the potential to adopt non-B DNA conformations. Genes harboring non-B DNA structure-forming sequences increase the risk of genetic instability and thus are associated with human diseases. In this review, we discuss putative mechanisms responsible for genetic instability events occurring at these non-B DNA structures, with a focus on hairpins, left-handed Z-DNA, and intramolecular triplexes or H-DNA. Slippage and misalignment are the most common events leading to DNA structure-induced mutagenesis. However, a number of other mechanisms of genetic instability have been proposed based on the finding that these structures not only induce expansions and deletions, but can also induce DNA strand breaks and rearrangements. The available data implicate a variety of proteins, such as mismatch repair proteins, nucleotide excision repair proteins, topoisomerases, and structure specific-nucleases in the processing of these mutagenic DNA structures. The potential mechanisms of genetic instability induced by these structures and their contribution to human diseases are discussed.
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Affiliation(s)
- Guliang Wang
- Department of Carcinogenesis, University of Texas M.D. Anderson Cancer Center, Science Park-Research Division, 1808 Park Road 1-C, P.O. Box 389, Smithville, 78957, USA
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48
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Gunderson CW, Segall AM. DNA repair, a novel antibacterial target: Holliday junction-trapping peptides induce DNA damage and chromosome segregation defects. Mol Microbiol 2006; 59:1129-48. [PMID: 16430689 DOI: 10.1111/j.1365-2958.2005.05009.x] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Holliday junction intermediates arise in several central pathways of DNA repair, replication fork restart, and site-specific recombination catalysed by tyrosine recombinases. Previously identified hexapeptide inhibitors of phage lambda integrase-mediated recombination block the resolution of Holliday junction intermediates in vitro and thereby inhibit recombination, but have no DNA cleavage activity themselves. The most potent peptides are specific for the branched DNA structure itself, as opposed to the integrase complex. Based on this activity, the peptides inhibit several unrelated Holliday junction-processing enzymes in vitro, including the RecG helicase and RuvABC junction resolvase complex. We have found that some of these hexapeptides are potent bactericidal antimicrobials, effective against both Gm+ and Gm- bacteria. Using epifluorescence microscopy and flow cytometry, we have characterized extensively the physiology of bacterial cells treated with these peptides. The hexapeptides cause DNA segregation abnormalities, filamentation and DNA damage. Damage caused by the peptides induces the SOS response, and is synergistic with damage caused by UV and mitomycin C. Our results are consistent with the model that the hexapeptides affect DNA targets that arise during recombination-dependent repair. We propose that the peptides trap intermediates in the repair of collapsed replication forks, preventing repair and resulting in bacterial death. Inhibition of DNA repair constitutes a novel target of antibiotic therapy. The peptides affect targets that arise in multiple pathways, and as expected, are quite resistant to the development of spontaneous antibiotic resistance.
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Affiliation(s)
- Carl W Gunderson
- Center for Microbial Sciences and Department of Biology, San Diego State University, San Diego, CA 92182-4614, USA
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49
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Ohtani S, Shinkai Y, Horibe A, Katayama K, Tsuji T, Matsushima Y, Tachibana M, Kunieda T. A Deletion in the Endothelin-B Receptor Gene is Responsible for the Waardenburg Syndrome-Like Phenotypes of WS4 Mice. Exp Anim 2006; 55:491-5. [PMID: 17090968 DOI: 10.1538/expanim.55.491] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
The WS4 mouse is an animal model for human Waardenburg syndrome type 4 (WS4), showing pigmentation anomalies, deafness and megacolon, which are caused by defects of neural crest-derived cells. We have previously reported that the gene responsible for the WS4 mouse is an allele of the piebald mutations of the endothelin B receptor gene (Ednrb). In this study, we examined the genomic sequence of the Ednrb gene in WS4 mice and found a 598-bp deletion in the gene. The deleted region contains the entire region of exon 2 and the 5' part of exon 3 and is flanked by inverted repeat sequences which are suggested to trigger the deletion. We concluded that the deletion in the Ednrb gene is the causative mutation for the phenotype of WS4 mice.
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Affiliation(s)
- Shin Ohtani
- Graduate School of Natural Science and Technology, Okayama University, Okayama, Japan
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50
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Lewis SM, Chen S, Strathern JN, Rattray AJ. New approaches to the analysis of palindromic sequences from the human genome: evolution and polymorphism of an intronic site at the NF1 locus. Nucleic Acids Res 2005; 33:e186. [PMID: 16340004 PMCID: PMC1310899 DOI: 10.1093/nar/gni189] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The nature of any long palindrome that might exist in the human genome is obscured by the instability of such sequences once cloned in Escherichia coli. We describe and validate a practical alternative to the analysis of naturally-occurring palindromes based upon cloning and propagation in Saccharomyces cerevisiae. With this approach we have investigated an intronic sequence in the human Neurofibromatosis 1 (NF1) locus that is represented by multiple conflicting versions in GenBank. We find that the site is highly polymorphic, exhibiting different degrees of palindromy in different individuals. A side-by-side comparison of the same plasmids in E.coli versus. S.cerevisiae demonstrated that the more palindromic alleles were inevitably corrupted upon cloning in E.coli, but could be propagated intact in yeast. The high quality sequence obtained from the yeast-based approach provides insight into the various mechanisms that destabilize a palindrome in E.coli, yeast and humans, into the diversification of a highly polymorphic site within the NF1 locus during primate evolution, and into the association between palindromy and chromosomal translocation.
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Affiliation(s)
- Susanna M Lewis
- Program in Genetics and Genomic Biology, Hospital for Sick Children Research Institute, Toronto, ON, Canada.
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