1
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Kosek D, Hickman AB, Ghirlando R, He S, Dyda F. Structures of ISCth4 transpososomes reveal the role of asymmetry in copy-out/paste-in DNA transposition. EMBO J 2021; 40:e105666. [PMID: 33006208 PMCID: PMC7780238 DOI: 10.15252/embj.2020105666] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2020] [Revised: 08/07/2020] [Accepted: 09/10/2020] [Indexed: 01/23/2023] Open
Abstract
Copy-out/paste-in transposition is a major bacterial DNA mobility pathway. It contributes significantly to the emergence of antibiotic resistance, often by upregulating expression of downstream genes upon integration. Unlike other transposition pathways, it requires both asymmetric and symmetric strand transfer steps. Here, we report the first structural study of a copy-out/paste-in transposase and demonstrate its ability to catalyze all pathway steps in vitro. X-ray structures of ISCth4 transposase, a member of the IS256 family of insertion sequences, bound to DNA substrates corresponding to three sequential steps in the reaction reveal an unusual asymmetric dimeric transpososome. During transposition, an array of N-terminal domains binds a single transposon end while the catalytic domain moves to accommodate the varying substrates. These conformational changes control the path of DNA flanking the transposon end and the generation of DNA-binding sites. Our results explain the asymmetric outcome of the initial strand transfer and show how DNA binding is modulated by the asymmetric transposase to allow the capture of a second transposon end and to integrate a circular intermediate.
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Affiliation(s)
- Dalibor Kosek
- Laboratory of Molecular BiologyNational Institute of Diabetes and Digestive and Kidney DiseasesNational Institutes of HealthBethesdaMDUSA
| | - Alison B Hickman
- Laboratory of Molecular BiologyNational Institute of Diabetes and Digestive and Kidney DiseasesNational Institutes of HealthBethesdaMDUSA
| | - Rodolfo Ghirlando
- Laboratory of Molecular BiologyNational Institute of Diabetes and Digestive and Kidney DiseasesNational Institutes of HealthBethesdaMDUSA
| | - Susu He
- Laboratory of Molecular BiologyNational Institute of Diabetes and Digestive and Kidney DiseasesNational Institutes of HealthBethesdaMDUSA
- Present address:
State Key Laboratory of Pharmaceutical BiotechnologyMedical School of Nanjing UniversityNanjingJiangsuChina
| | - Fred Dyda
- Laboratory of Molecular BiologyNational Institute of Diabetes and Digestive and Kidney DiseasesNational Institutes of HealthBethesdaMDUSA
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2
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Chevignon G, Periquet G, Gyapay G, Vega-Czarny N, Musset K, Drezen JM, Huguet E. Cotesia congregata Bracovirus Circles Encoding PTP and Ankyrin Genes Integrate into the DNA of Parasitized Manduca sexta Hemocytes. J Virol 2018; 92:e00438-18. [PMID: 29769342 PMCID: PMC6052314 DOI: 10.1128/jvi.00438-18] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2018] [Accepted: 05/04/2018] [Indexed: 12/21/2022] Open
Abstract
Polydnaviruses (PDVs) are essential for the parasitism success of tens of thousands of species of parasitoid wasps. PDVs are present in wasp genomes as proviruses, which serve as the template for the production of double-stranded circular viral DNA carrying virulence genes that are injected into lepidopteran hosts. PDV circles do not contain genes coding for particle production, thereby impeding viral replication in caterpillar hosts during parasitism. Here, we investigated the fate of PDV circles of Cotesia congregata bracovirus during parasitism of the tobacco hornworm, Manduca sexta, by the wasp Cotesia congregata Sequences sharing similarities with host integration motifs (HIMs) of Microplitis demolitor bracovirus (MdBV) circles involved in integration into DNA could be identified in 12 CcBV circles, which encode PTP and VANK gene families involved in host immune disruption. A PCR approach performed on a subset of these circles indicated that they persisted in parasitized M. sexta hemocytes as linear forms, possibly integrated in host DNA. Furthermore, by using a primer extension capture method based on these HIMs and high-throughput sequencing, we could show that 8 out of 9 circles tested were integrated in M. sexta hemocyte genomic DNA and that integration had occurred specifically using the HIM, indicating that an HIM-mediated specific mechanism was involved in their integration. Investigation of BV circle insertion sites at the genome scale revealed that certain genomic regions appeared to be enriched in BV insertions, but no specific M. sexta target site could be identified.IMPORTANCE The identification of a specific and efficient integration mechanism shared by several bracovirus species opens the question of its role in braconid parasitoid wasp parasitism success. Indeed, results obtained here show massive integration of bracovirus DNA in somatic immune cells at each parasitism event of a caterpillar host. Given that bracoviruses do not replicate in infected cells, integration of viral sequences in host DNA might allow the production of PTP and VANK virulence proteins within newly dividing cells of caterpillar hosts that continue to develop during parasitism. Furthermore, this integration process could serve as a basis to understand how PDVs mediate the recently identified gene flux between parasitoid wasps and Lepidoptera and the frequency of these horizontal transfer events in nature.
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Affiliation(s)
- Germain Chevignon
- Institut de Recherche sur la Biologie de l'Insecte, CNRS UMR 7261, Université de Tours, Tours, France
| | - Georges Periquet
- Institut de Recherche sur la Biologie de l'Insecte, CNRS UMR 7261, Université de Tours, Tours, France
| | - Gabor Gyapay
- Commissariat à l'Energie Atomique et aux Energies Alternatives, Genoscope (Centre National de Séquençage), Evry, France
| | - Nathalie Vega-Czarny
- Commissariat à l'Energie Atomique et aux Energies Alternatives, Genoscope (Centre National de Séquençage), Evry, France
| | - Karine Musset
- Institut de Recherche sur la Biologie de l'Insecte, CNRS UMR 7261, Université de Tours, Tours, France
| | - Jean-Michel Drezen
- Institut de Recherche sur la Biologie de l'Insecte, CNRS UMR 7261, Université de Tours, Tours, France
| | - Elisabeth Huguet
- Institut de Recherche sur la Biologie de l'Insecte, CNRS UMR 7261, Université de Tours, Tours, France
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3
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Abstract
IS911 has provided a powerful model for studying the transposition of members of a large class of transposable element: the IS3 family of bacterial Insertion Sequences (IS). These transpose by a Copy-out-Paste-in mechanism in which a double-strand IS circle transposition intermediate is generated from the donor site by replication and proceeds to integrate into a suitable double strand DNA target. This is perhaps one of the most common transposition mechanisms known to date. Copy-out-Paste-in transposition has been adopted by members of at least eight large IS families. This chapter details the different steps of the Copy-out-Paste-in mechanism involved in IS911 transposition. At a more biological level it also describes various aspects of regulation of the transposition process. These include transposase production by programmed translational frameshifting, transposase expression from the circular intermediate using a specialized promoter assembled at the circle junction and binding of the nascent transposase while it remains attached to the ribosome during translation (co-translational binding). This co-translational binding of the transposase to neighboring IS ends provides an explanation for the longstanding observation that transposases show a cis-preference for their activities.
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4
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Abstract
DNA transposases are enzymes that catalyze the movement of discrete pieces of DNA from one location in the genome to another. Transposition occurs through a series of controlled DNA strand cleavage and subsequent integration reactions that are carried out by nucleoprotein complexes known as transpososomes. Transpososomes are dynamic assemblies which must undergo conformational changes that control DNA breaks and ensure that, once started, the transposition reaction goes to completion. They provide a precise architecture within which the chemical reactions involved in transposon movement occur, but adopt different conformational states as transposition progresses. Their components also vary as they must, at some stage, include target DNA and sometimes even host-encoded proteins. A very limited number of transpososome states have been crystallographically captured, and here we provide an overview of the various structures determined to date. These structures include examples of DNA transposases that catalyze transposition by a cut-and-paste mechanism using an RNaseH-like nuclease catalytic domain, those that transpose using only single-stranded DNA substrates and targets, and the retroviral integrases that carry out an integration reaction very similar to DNA transposition. Given that there are a number of common functional requirements for transposition, it is remarkable how these are satisfied by complex assemblies that are so architecturally different.
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5
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Duval-Valentin G, Chandler M. Cotranslational control of DNA transposition: a window of opportunity. Mol Cell 2012; 44:989-96. [PMID: 22195971 DOI: 10.1016/j.molcel.2011.09.027] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2011] [Revised: 06/17/2011] [Accepted: 09/30/2011] [Indexed: 10/14/2022]
Abstract
Transposable elements are important in genome dynamics and evolution. Bacterial insertion sequences (IS) constitute a major group in number and impact. Understanding their role in shaping genomes requires knowledge of how their transposition activity is regulated and interfaced with the host cell. One IS regulatory phenomenon is a preference of their transposases (Tpases) for action on the element from which they are expressed (cis) rather than on other copies of the same element (trans). Using IS911, we show in vivo that activity in cis was ~200 fold higher than in trans. We also demonstrate that a translational frameshifting pause signal influences cis preference presumably by facilitating sequential folding and cotranslational binding of the Tpase. In vitro, IS911 Tpase bound IS ends during translation but not after complete translation. Cotranslational binding of nascent Tpase permits tight control of IS proliferation providing a mechanistic explanation for cis regulation of transposition involving an unexpected partner, the ribosome.
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Affiliation(s)
- Guy Duval-Valentin
- Laboratoire de Microbiologie et Génétique Moléculaires, CNRS UMR5100, Campus Université Paul Sabatier, 118 Route de Narbonne, F31062 Toulouse Cedex, France
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Lewis LA, Astatke M, Umekubo PT, Alvi S, Saby R, Afrose J, Oliveira PH, Monteiro GA, Prazeres DM. Protein-DNA interactions define the mechanistic aspects of circle formation and insertion reactions in IS2 transposition. Mob DNA 2012; 3:1. [PMID: 22277150 PMCID: PMC3299598 DOI: 10.1186/1759-8753-3-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2011] [Accepted: 01/26/2012] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Transposition in IS3, IS30, IS21 and IS256 insertion sequence (IS) families utilizes an unconventional two-step pathway. A figure-of-eight intermediate in Step I, from asymmetric single-strand cleavage and joining reactions, is converted into a double-stranded minicircle whose junction (the abutted left and right ends) is the substrate for symmetrical transesterification attacks on target DNA in Step II, suggesting intrinsically different synaptic complexes (SC) for each step. Transposases of these ISs bind poorly to cognate DNA and comparative biophysical analyses of SC I and SC II have proven elusive. We have prepared a native, soluble, active, GFP-tagged fusion derivative of the IS2 transposase that creates fully formed complexes with single-end and minicircle junction (MCJ) substrates and used these successfully in hydroxyl radical footprinting experiments. RESULTS In IS2, Step I reactions are physically and chemically asymmetric; the left imperfect, inverted repeat (IRL), the exclusive recipient end, lacks donor function. In SC I, different protection patterns of the cleavage domains (CDs) of the right imperfect inverted repeat (IRR; extensive in cis) and IRL (selective in trans) at the single active cognate IRR catalytic center (CC) are related to their donor and recipient functions. In SC II, extensive binding of the IRL CD in trans and of the abutted IRR CD in cis at this CC represents the first phase of the complex. An MCJ substrate precleaved at the 3' end of IRR revealed a temporary transition state with the IRL CD disengaged from the protein. We propose that in SC II, sequential 3' cleavages at the bound abutted CDs trigger a conformational change, allowing the IRL CD to complex to its cognate CC, producing the second phase. Corroborating data from enhanced residues and curvature propensity plots suggest that CD to CD interactions in SC I and SC II require IRL to assume a bent structure, to facilitate binding in trans. CONCLUSIONS Different transpososomes are assembled in each step of the IS2 transposition pathway. Recipient versus donor end functions of the IRL CD in SC I and SC II and the conformational change in SC II that produces the phase needed for symmetrical IRL and IRR donor attacks on target DNA highlight the differences.
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Affiliation(s)
- Leslie A Lewis
- Department of Biology, York College of the City University of New York, Jamaica, New York 11451, USA.
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7
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Lewis LA, Astatke M, Umekubo PT, Alvi S, Saby R, Afrose J. Soluble expression, purification and characterization of the full length IS2 Transposase. Mob DNA 2011; 2:14. [PMID: 22032517 PMCID: PMC3219604 DOI: 10.1186/1759-8753-2-14] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2011] [Accepted: 10/27/2011] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The two-step transposition pathway of insertion sequences of the IS3 family, and several other families, involves first the formation of a branched figure-of-eight (F-8) structure by an asymmetric single strand cleavage at one optional donor end and joining to the flanking host DNA near the target end. Its conversion to a double stranded minicircle precedes the second insertional step, where both ends function as donors. In IS2, the left end which lacks donor function in Step I acquires it in Step II. The assembly of two intrinsically different protein-DNA complexes in these F-8 generating elements has been intuitively proposed, but a barrier to testing this hypothesis has been the difficulty of isolating a full length, soluble and active transposase that creates fully formed synaptic complexes in vitro with protein bound to both binding and catalytic domains of the ends. We address here a solution to expressing, purifying and structurally analyzing such a protein. RESULTS A soluble and active IS2 transposase derivative with GFP fused to its C-terminus functions as efficiently as the native protein in in vivo transposition assays. In vitro electrophoretic mobility shift assay data show that the partially purified protein prepared under native conditions binds very efficiently to cognate DNA, utilizing both N- and C-terminal residues. As a precursor to biophysical analyses of these complexes, a fluorescence-based random mutagenesis protocol was developed that enabled a structure-function analysis of the protein with good resolution at the secondary structure level. The results extend previous structure-function work on IS3 family transposases, identifying the binding domain as a three helix H + HTH bundle and explaining the function of an atypical leucine zipper-like motif in IS2. In addition gain- and loss-of-function mutations in the catalytic active site define its role in regional and global binding and identify functional signatures that are common to the three dimensional catalytic core motif of the retroviral integrase superfamily. CONCLUSIONS Intractably insoluble transposases, such as the IS2 transposase, prepared by solubilization protocols are often refractory to whole protein structure-function studies. The results described here have validated the use of GFP-tagging and fluorescence-based random mutagenesis in overcoming this limitation at the secondary structure level.
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Affiliation(s)
- Leslie A Lewis
- Department of Biology, York College of the City University of New York, Jamaica, New York, 11451, USA
- Program in Cellular, Molecular and Developmental Biology, Graduate Center, City University of New York, New York, New York 11016, USA
| | - Mekbib Astatke
- Johns Hopkins University, Applied Physics Laboratory, Laurel, MD 20723, USA
| | - Peter T Umekubo
- Department of Biology, York College of the City University of New York, Jamaica, New York, 11451, USA
- Accera Inc, Broomfield, CO 80021, USA
| | - Shaheen Alvi
- Department of Biology, York College of the City University of New York, Jamaica, New York, 11451, USA
- Ross Medical School, Roseau, Dominica
| | - Robert Saby
- Department of Biology, York College of the City University of New York, Jamaica, New York, 11451, USA
- Department of Occupational Therapy, York College of the City University of New York, Jamaica, New York, 11451, USA
| | - Jehan Afrose
- Department of Biology, York College of the City University of New York, Jamaica, New York, 11451, USA
- Skirball Institute of Biomolecular Medicine, New York University School of Medicine, New York, New York, 10016, USA
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8
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Rousseau P, Tardin C, Tolou N, Salomé L, Chandler M. A model for the molecular organisation of the IS911 transpososome. Mob DNA 2010; 1:16. [PMID: 20553579 PMCID: PMC2909936 DOI: 10.1186/1759-8753-1-16] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2010] [Accepted: 06/16/2010] [Indexed: 11/10/2022] Open
Abstract
Tight regulation of transposition activity is essential to limit damage transposons may cause by generating potentially lethal DNA rearrangements. Assembly of a bona fide protein-DNA complex, the transpososome, within which transposition is catalysed, is a crucial checkpoint in this regulation. In the case of IS911, a member of the large IS3 bacterial insertion sequence family, the transpososome (synaptic complex A; SCA) is composed of the right and left inverted repeated DNA sequences (IRR and IRL) bridged by the transposase, OrfAB (the IS911-encoded enzyme that catalyses transposition). To characterise further this important protein-DNA complex in vitro, we used different tagged and/or truncated transposase forms and analysed their interaction with IS911 ends using gel electrophoresis. Our results allow us to propose a model in which SCA is assembled with a dimeric form of the transposase. Furthermore, we present atomic force microscopy results showing that the terminal inverted repeat sequences are probably assembled in a parallel configuration within the SCA. These results represent the first step in the structural description of the IS911 transpososome, and are discussed in comparison with the very few other transpososome examples described in the literature.
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Affiliation(s)
- Philippe Rousseau
- Centre National de la Recherche Scientifique, LMGM, F-31000 Toulouse, France.
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9
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Characterization of the transposase encoded by IS256, the prototype of a major family of bacterial insertion sequence elements. J Bacteriol 2010; 192:4153-63. [PMID: 20543074 DOI: 10.1128/jb.00226-10] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
IS256 is the founding member of the IS256 family of insertion sequence (IS) elements. These elements encode a poorly characterized transposase, which features a conserved DDE catalytic motif and produces circular IS intermediates. Here, we characterized the IS256 transposase as a DNA-binding protein and obtained insight into the subdomain organization and functional properties of this prototype enzyme of IS256 family transposases. Recombinant forms of the transposase were shown to bind specifically to inverted repeats present in the IS256 noncoding regions. A DNA-binding domain was identified in the N-terminal part of the transposase, and a mutagenesis study targeting conserved amino acid residues in this region revealed a putative helix-turn-helix structure as a key element involved in DNA binding. Furthermore, we obtained evidence to suggest that the terminal nucleotides of IS256 are critically involved in IS circularization. Although small deletions at both ends reduced the formation of IS circles, changes at the left-hand IS256 terminus proved to be significantly more detrimental to circle production. Taken together, the data lead us to suggest that the IS256 transposase-mediated circularization reaction preferentially starts with a sequence-specific first-strand cleavage at the left-hand IS terminus.
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10
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Abstract
The mobile element IS30 has 26-bp imperfect terminal inverted repeats (IRs) that are indispensable for transposition. We have analyzed the effects of IR mutations on both major transposition steps, the circle formation and integration of the abutted ends, characteristic for IS30. Several mutants show strikingly different phenotypes if the mutations are present at one or both ends and differentially influence the transposition steps. The two IRs are equivalent in the recombination reactions and contain several functional regions. We have determined that positions 20 to 26 are responsible for binding of the N-terminal domain of the transposase and the formation of a correct 2-bp spacer between the abutted ends. However, integration is efficient without this region, suggesting that a second binding site for the transposase may exist, possibly within the region from 4 to 11 bp. Several mutations at this part of the IRs, which are highly conserved in the IS30 family, considerably affected both major transposition steps. In addition, positions 16 and 17 seem to be responsible for distinguishing the IRs of related insertion sequences by providing specificity for the transposase to recognize its cognate ends. Finally, we show both in vivo and in vitro that position 3 has a determining role in the donor function of the ends, especially in DNA cleavage adjacent to the IRs. Taken together, the present work provides evidence for a more complex organization of the IS30 IRs than was previously suggested.
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11
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The genome sequence of Psychrobacter arcticus 273-4, a psychroactive Siberian permafrost bacterium, reveals mechanisms for adaptation to low-temperature growth. Appl Environ Microbiol 2010; 76:2304-12. [PMID: 20154119 DOI: 10.1128/aem.02101-09] [Citation(s) in RCA: 132] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Psychrobacter arcticus strain 273-4, which grows at temperatures as low as -10 degrees C, is the first cold-adapted bacterium from a terrestrial environment whose genome was sequenced. Analysis of the 2.65-Mb genome suggested that some of the strategies employed by P. arcticus 273-4 for survival under cold and stress conditions are changes in membrane composition, synthesis of cold shock proteins, and the use of acetate as an energy source. Comparative genome analysis indicated that in a significant portion of the P. arcticus proteome there is reduced use of the acidic amino acids and proline and arginine, which is consistent with increased protein flexibility at low temperatures. Differential amino acid usage occurred in all gene categories, but it was more common in gene categories essential for cell growth and reproduction, suggesting that P. arcticus evolved to grow at low temperatures. Amino acid adaptations and the gene content likely evolved in response to the long-term freezing temperatures (-10 degrees C to -12 degrees C) of the Kolyma (Siberia) permafrost soil from which this strain was isolated. Intracellular water likely does not freeze at these in situ temperatures, which allows P. arcticus to live at subzero temperatures.
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12
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Bias between the left and right inverted repeats during IS911 targeted insertion. J Bacteriol 2008; 190:6111-8. [PMID: 18586933 DOI: 10.1128/jb.00452-08] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
IS911 is a bacterial insertion sequence composed of two consecutive overlapping open reading frames (ORFs [orfA and orfB]) encoding the transposase (OrfAB) as well as a regulatory protein (OrfA). These ORFs are bordered by terminal left and right inverted repeats (IRL and IRR, respectively) with several differences in nucleotide sequence. IS911 transposition is asymmetric: each end is cleaved on one strand to generate a free 3'-OH, which is then used as the nucleophile in attacking the opposite insertion sequence (IS) end to generate a free IS circle. This will be inserted into a new target site. We show here that the ends exhibit functional differences which, in vivo, may favor the use of one compared to the other during transposition. Electromobility shift assays showed that a truncated form of the transposase [OrfAB(1-149)] exhibits higher affinity for IRR than for IRL. While there was no detectable difference in IR activities during the early steps of transposition, IRR was more efficient during the final insertion steps. We show here that the differential activities between the two IRs correlate with the different affinities of OrfAB(1-149) for the IRs during assembly of the nucleoprotein complexes leading to transposition. We conclude that the two inverted repeats are not equivalent during IS911 transposition and that this asymmetry may intervene to determine the ordered assembly of the different protein-DNA complexes involved in the reaction.
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13
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Szabó M, Kiss J, Nagy Z, Chandler M, Olasz F. Sub-terminal sequences modulating IS30 transposition in vivo and in vitro. J Mol Biol 2007; 375:337-52. [PMID: 18022196 DOI: 10.1016/j.jmb.2007.10.043] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2007] [Revised: 10/12/2007] [Accepted: 10/16/2007] [Indexed: 11/18/2022]
Abstract
Inverted repeats of insertion sequences (ISs) are indispensable for transposition. We demonstrate that sub-terminal sequences adjacent to the inverted repeats of IS30 are also required for optimal transposition activity. We have developed a cell-free recombination system and showed that the transposase catalyses formation of a figure-of-eight transposition intermediate, where a 2 bp long single strand bridge holds the inverted repeat sequences (IRs) together. This is the first demonstration of the figure-of-eight structure in a non-IS3 family element, suggesting that this mechanism is likely more widely adopted among IS families. We show that the absence of sub-terminal IS30 sequences negatively influences figure-of-eight production both in vivo and in vitro. These regions enhance IR-IR junction formation and IR-targeting events in vivo. Enhancer elements have been identified within 51 bp internal to IRL and 17 bp internal to IRR. In the right end, a decanucleotide, 5'-GAGATAATTG-3', is responsible for wild-type activity, while in the left end, a complex assembly of repetitive elements is required. Functioning of the 10 bp element in the right end is position-dependent and the repetitive elements in the left end act cooperatively and may influence bendability of the end. In vitro kinetic experiments suggest that the sub-terminal enhancers may, at least partly, be transposase-dependent. Such enhancers may reflect a subtle regulatory mechanism for IS30 transposition.
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MESH Headings
- Base Sequence
- Binding Sites
- Cell-Free System
- DNA Mutational Analysis
- DNA Primers
- DNA Transposable Elements
- DNA, Bacterial/chemistry
- DNA, Bacterial/genetics
- DNA, Bacterial/isolation & purification
- DNA, Circular/genetics
- Dimerization
- Electrophoresis, Polyacrylamide Gel
- Enhancer Elements, Genetic
- Escherichia coli/genetics
- Genes, Bacterial
- In Vitro Techniques
- Kinetics
- Models, Genetic
- Models, Molecular
- Molecular Sequence Data
- Mutagenesis, Insertional
- Nucleic Acid Conformation
- Open Reading Frames
- Plasmids
- Point Mutation
- Polymerase Chain Reaction
- Recombination, Genetic
- Salmonella typhimurium/genetics
- Terminal Repeat Sequences
- Transposases/chemistry
- Transposases/genetics
- Transposases/isolation & purification
- Transposases/metabolism
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Affiliation(s)
- Mónika Szabó
- Agricultural Biotechnology Center, 4 Szent-Györgyi Albert str., H-2100, Gödöllo, Hungary
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14
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Rousseau P, Loot C, Guynet C, Ah-Seng Y, Ton-Hoang B, Chandler M. Control of IS911 target selection: how OrfA may ensure IS dispersion. Mol Microbiol 2007; 63:1701-9. [PMID: 17367389 DOI: 10.1111/j.1365-2958.2007.05615.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
IS911 transposition involves a closed circular insertion sequence intermediate (IS-circle) and two IS-encoded proteins: the transposase OrfAB and OrfA which regulates IS911 insertion. OrfAB alone promotes insertion preferentially next to DNA sequences resembling IS911 ends while the addition of OrfA strongly stimulates insertion principally into DNA targets devoid of the IS911 end sequences. OrfAB shares its N-terminal region with OrfA. This includes a helix-turn-helix (HTH) motif and the first three of four heptads of a leucine zipper (LZ). OrfAB binds specifically to IS911 ends via its HTH whereas OrfA does not. We show here: that OrfA binds DNA non-specifically and that this requires the HTH; that OrfA LZ is required for its multimerization; and that both motifs are essential for OrfA activity. We propose that these OrfA properties are required to assemble a nucleoprotein complex committed to random IS911 insertion. This control of IS911 insertion activity by OrfA in this way would assure its dispersion.
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Affiliation(s)
- Philippe Rousseau
- Laboratoire de Microbiologie et Génétique Moléculaire (UMR 5100 CNRS - U.Toulouse-3), 118 rte. de Narbonne, Bât. IBCG, 31062 Toulouse Cedex 09, France.
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15
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Bouet JY, Bouvier M, Lane D. Concerted action of plasmid maintenance functions: partition complexes create a requirement for dimer resolution. Mol Microbiol 2006; 62:1447-59. [PMID: 17059567 DOI: 10.1111/j.1365-2958.2006.05454.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Partition of prokaryotic DNA requires formation of specific protein-centromere complexes, but an excess of the protein can disrupt segregation. The mechanisms underlying this destabilization are unknown. We have found that destabilization by the F plasmid partition protein, SopB, of plasmids carrying the F centromere, sopC, results from the capacity of the SopB-sopC partition complex to stimulate plasmid multimerization. Mutant SopBs unable to destabilize failed to increase multimerization. Stability of wild-type mini-F, whose ResD/rfsF site-specific recombination system enables it to resolve multimers to monomers, was barely affected by excess SopB. Destabilization of plasmids lacking the rfsF site was suppressed by recF, recO and recR, but not by recB, mutant alleles, indicating that multimerization is initiated from single-strand gaps. SopB did not alter the amounts or distribution of replication intermediates, implying that SopB-DNA complexes do not create single-strand gaps by blocking replication forks. Rather, the results are consistent with SopB-DNA complexes channelling gapped molecules into the RecFOR recombination pathway. We suggest that extended SopB-DNA complexes increase the likelihood of recombination between sibling plasmids by keeping them in close contact prior to SopA-mediated segregation. These results cast plasmid site-specific resolution in a new role - compensation for untoward consequences of partition complex formation.
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Affiliation(s)
- Jean-Yves Bouet
- Laboratoire de Microbiologie et Génétique Moléculaire, Centre National de Recherche, Scientifique, Faculté Université Paul Sabatier, 118 Route de Narbonne, 31062 Toulouse, France
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16
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Pouget N, Turlan C, Destainville N, Salomé L, Chandler M. IS911 transpososome assembly as analysed by tethered particle motion. Nucleic Acids Res 2006; 34:4313-23. [PMID: 16923775 PMCID: PMC1636345 DOI: 10.1093/nar/gkl420] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Initiation of transposition requires formation of a synaptic complex between both transposon ends and the transposase (Tpase), the enzyme which catalyses DNA cleavage and strand transfer and which ensures transposon mobility. We have used a single-molecule approach, tethered particle motion (TPM), to observe binding of a Tpase derivative, OrfAB[149], amputated for its C-terminal catalytic domain, to DNA molecules carrying one or two IS911 ends. Binding of OrfAB[149] to a single IS911 end provoked a small shortening of the DNA. This is consistent with a DNA bend introduced by protein binding to a single end. This was confirmed using a classic gel retardation assay with circularly permuted DNA substrates. When two ends were present on the tethered DNA in their natural, inverted, configuration, Tpase not only provoked the short reduction in length but also generated species with greatly reduce effective length consistent with DNA looping between the ends. Once formed, this 'looped' species was very stable. Kinetic analysis in real-time suggested that passage from the bound unlooped to the looped state could involve another species of intermediate length in which both transposon ends are bound. DNA carrying directly repeated ends also gave rise to the looped species but the level of the intermediate species was significantly enhanced. Its accumulation could reflect a less favourable synapse formation from this configuration than for the inverted ends. This is compatible with a model in which Tpase binds separately to and bends each end (the intermediate species) and protein-protein interactions then lead to synapsis (the looped species).
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Affiliation(s)
- N. Pouget
- Laboratoire de Microbiologie et Génétique Moléculaire (UMR CNRS 5100)118 route de Narbonne, 31062 Toulouse cedex, France
- Institut de Pharmacologie et Biologie Structurale (UMR CNRS 5089)205 route de Narbonne 31077 Toulouse cedex, France
| | - C. Turlan
- Laboratoire de Microbiologie et Génétique Moléculaire (UMR CNRS 5100)118 route de Narbonne, 31062 Toulouse cedex, France
| | - N. Destainville
- Laboratoire de Physique Théorique (UMR CNRS 5152), IRSAMC, Université Paul Sabatier118 route de Narbonne, 31062 Toulouse cedex, France
| | - L. Salomé
- Institut de Pharmacologie et Biologie Structurale (UMR CNRS 5089)205 route de Narbonne 31077 Toulouse cedex, France
| | - M. Chandler
- Laboratoire de Microbiologie et Génétique Moléculaire (UMR CNRS 5100)118 route de Narbonne, 31062 Toulouse cedex, France
- To whom correspondence should be addressed. Tel: +33 5 61 33 58 61; Fax: +33 5 61 33 58 58.
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17
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Brillet B, Benjamin B, Bigot Y, Yves B, Augé-Gouillou C, Corinne AG. Assembly of the Tc1 and mariner transposition initiation complexes depends on the origins of their transposase DNA binding domains. Genetica 2006; 130:105-20. [PMID: 16912840 DOI: 10.1007/s10709-006-0025-2] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2006] [Accepted: 06/02/2006] [Indexed: 01/20/2023]
Abstract
In this review, we focus on the assembly of DNA/protein complexes that trigger transposition in eukaryotic members of the IS630-Tc1-mariner (ITm) super-family, the Tc1- and mariner-like elements (TLEs and MLEs). Elements belonging to this super-family encode transposases with DNA binding domains of different origins, and recent data indicate that the chimerization of functional domains has been an important evolutionary aspect in the generation of new transposons within the ITm super-family. These data also reveal that the inverted terminal repeats (ITRs) at the ends of transposons contain three kinds of motif within their sequences. The first two are well known and correspond to the cleavage site on the outer ITR extremities, and the transposase DNA binding site. The organization of ITRs and of the transposase DNA binding domains implies that differing pathways are used by MLEs and TLEs to regulate transposition initiation. These differences imply that the ways ITRs are recognized also differ leading to the formation of differently organized synaptic complexes. The third kind of motif is the transposition enhancers, which have been found in almost all the functional MLEs and TLEs analyzed to date. Finally, in vitro and in vivo assays of various elements all suggest that the transposition initiation complex is not formed randomly, but involves a mechanism of oriented transposon scanning.
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Affiliation(s)
- Benjamin Brillet
- Laboratoire d'Etudes des Parasites Génétiques, Université François Rabelais, FRE CNRS 2969, UFR Sciences & Techniques, Parc Grandmont, 37200, Tours, France
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18
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Abstract
The mobility of transposable elements via a cut-and-paste mechanism depends on the elaboration of a nucleoprotein complex known as the synaptic complex. We show here that the Mos1 synaptic complex consists of the two inverted terminal repeats of the element brought together by a transposase tetramer and is designated paired-end complex 2 (PEC2). The assembly of PEC2 requires the formation of a simpler complex, containing one terminal repeat and two transposase molecules and designated single-end complex 2 (SEC2). In light of the formation of SEC2 and PEC2, we demonstrate the presence of two binding sites for the transposase within a single terminal repeat. We have found that the sequence of the Mos1 inverted terminal repeats contains overlapping palindromic and mirror motifs, which could account for the binding of two transposase molecules "side by side" on the same inverted terminal repeat. We provide data indicating that the Mos1 transposase dimer is formed within a single terminal repeat through a cooperative pathway. Finally, the concept of a tetrameric synaptic complex may simply account for the inability of a single mariner transposase molecule to interact at the same time with two kinds of DNA: the inverted repeat and the target DNA.
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Affiliation(s)
- Corinne Augé-Gouillou
- Laboratoire d'Etude des Parasites Génétiques, Université François Rabelais, EA 3868, UFR des Sciences et Techniques, BAtiment L, Parc de Grandmont, 37200 Tours, France.
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19
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Ton-Hoang B, Turlan C, Chandler M. Functional domains of the IS1 transposase: analysis in vivo and in vitro. Mol Microbiol 2005; 53:1529-43. [PMID: 15387827 DOI: 10.1111/j.1365-2958.2004.04223.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The IS1 bacterial insertion sequence family, considered to be restricted to Enterobacteria, has now been extended to other Eubacteria and to Archaebacteria, reviving interest in its study. To analyse the functional domains of the InsAB' transposase of IS1A, a representative of this family, we used an in vivo system which measures IS1-promoted rescue of a temperature-sensitive pSC101 plasmid by fusion with a pBR322::IS1 derivative. We also describe the partial purification of the IS1 transposase and the development of several in vitro assays for transposase activity. These included a DNA band shift assay, a transposase-mediated cleavage assay and an integration assay. Alignments of IS family members (http://www-is.biotoul.fr) not only confirmed the presence of an N-terminal helix-turn-helix and a C-terminal DDE motif in InsAB', but also revealed a putative N-terminal zinc finger. We have combined the in vitro and in vivo tests to carry out a functional analysis of InsAB' using a series of site-directed InsAB' mutants based on these alignments. The results demonstrate that appropriate mutations in the zinc finger and helix-turn-helix motifs result in loss of binding activity to the ends of IS1 whereas mutations in the DDE domain are affected in subsequent transposition steps but not in end binding.
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Affiliation(s)
- Bao Ton-Hoang
- Laboratoire de Microbiologie et de Génétique Moléculaire, CNRS, 118 route de Narbonne, 31062, Toulouse Cedex, France.
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20
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Abstract
The genes that encode immunoglobulins and T-cell receptors must be assembled from the multiple variable (V), joining (J), and sometimes diversity (D) gene segments present in the germline loci. This process of V(D)J recombination is the major source of the immense diversity of the immune repertoire of jawed vertebrates. The recombinase that initiates the process, recombination-activating genes 1 (RAG1) and RAG2, belongs to a large family that includes transposases and retroviral integrases. RAG1/2 cleaves the DNA adjacent to the gene segments to be recombined, and the segments are then joined together by DNA repair factors. A decade of biochemical research on RAG1/2 has revealed many similarities to transposition, culminating with the observation that RAG1/2 can carry out transpositional strand transfer. Here, we discuss the parallels between V(D)J recombination and transposition, focusing specifically on the assembly of the recombination nucleoprotein complex, the mechanism of cleavage, the disassembly of post-cleavage complexes, and aberrant reactions carried out by the recombinase that do not result in successful locus rearrangement and may be deleterious to the organism. This work highlights the considerable diversity of transposition systems and their relation to V(D)J recombination.
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Affiliation(s)
- Jessica M Jones
- Department of Biochemistry and Molecular Biology, Georgetown University Medical Center, Washington DC, USA
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21
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Turlan C, Loot C, Chandler M. IS911 partial transposition products and their processing by the Escherichia coli RecG helicase. Mol Microbiol 2004; 53:1021-33. [PMID: 15306008 DOI: 10.1111/j.1365-2958.2004.04165.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Insertion of bacterial insertion sequence IS911 can often be directed to sequences resembling its ends. We have investigated this type of transposition and shown that it can occur via cleavage of a single end and its targeted transfer next to another end. The single end transfer (SET) events generate branched DNA molecules that contain a nicked Holliday junction and can be considered as partial transposition products. Our results indicate that these can be processed by the Escherichia coli host independently of IS911-encoded proteins. Such resolution depends on the presence of homologous DNA regions neighbouring the cross-over point in the SET molecule. Processing is often accompanied by sequence conversion between donor and target sequences, suggesting that branch migration is involved. We show that resolution is greatly reduced in a recG host. Thus, the branched DNA-specific helicase, RecG, involved in processing of potentially lethal DNA structures such as stalled replication forks, also intervenes in the resolution of partial IS911 transposition products.
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Affiliation(s)
- Catherine Turlan
- Laboratoire de Microbiologie et Génétique Moléculaires, CNRS UMR5100, 118 Rte de Narbonne, F31062 Toulouse Cedex, France.
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22
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Rousseau P, Gueguen E, Duval-Valentin G, Chandler M. The helix-turn-helix motif of bacterial insertion sequence IS911 transposase is required for DNA binding. Nucleic Acids Res 2004; 32:1335-44. [PMID: 14981152 PMCID: PMC390272 DOI: 10.1093/nar/gkh276] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The transposase of IS911, a member of the IS3 family of bacterial insertion sequences, is composed of a catalytic domain located at its C-terminal end and a DNA binding domain located at its N-terminal end. Analysis of the transposases of over 60 members of the IS3 family revealed the presence of a helix-turn-helix (HTH) motif within the N-terminal region. Alignment of these potential secondary structures further revealed a completely conserved tryptophan residue similar to that found in the HTH motifs of certain homeodomain proteins. The analysis also uncovered a similarity between the IS3 family HTH and that of members of the LysR family of bacterial transcription factors. This information was used to design site-directed mutations permitting an assessment of its role in transposase function. A series of in vivo and in vitro tests demonstrated that the HTH domain is important in directing the transposase to bind the terminal inverted repeats of IS911.
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Affiliation(s)
- Philippe Rousseau
- Laboratoire de Microbiologie et de Génétique Moléculaire, CNRS, 118 Route de Narbonne, F-31062 Toulouse Cedex, France.
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23
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Tourand Y, Kobryn K, Chaconas G. Sequence-specific recognition but position-dependent cleavage of two distinct telomeres by the Borrelia burgdorferi telomere resolvase, ResT. Mol Microbiol 2003; 48:901-11. [PMID: 12753185 DOI: 10.1046/j.1365-2958.2003.03485.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
An unusual feature of bacteria in the genus Borrelia (causative agents of Lyme disease and relapsing fever) is a segmented genome consisting of multiple linear DNA molecules with covalently closed hairpin ends, known as telomeres. The hairpin telomeres are generated by a DNA breakage and reunion process (telomere resolution) promoted by ResT, an enzyme using an active site related to that of tyrosine recombinases and type IB topoisomerases. In this study, we define the minimal sequence requirements for a functional telomere and identify specific basepairs that appear to be important for telomere resolution. In addition, we show that the two naturally occurring and distinct telomere spacings found in B. burgdorferi can both be efficiently processed by ResT. This flexibility for substrate utilization by ResT supports the argument for a single telomere resolvase in Borrelia. Furthermore, although telomere recognition requires sequence specificity in part of the substrate, DNA cleavage is instead position dependent and occurs at a fixed distance from the axis of symmetry and the conserved sequence of box 3 in the different replicated telomere substrates. This positional dependence for DNA cleavage has not been observed previously for a tyrosine recombinase.
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Affiliation(s)
- Yvonne Tourand
- Department of Microbiology and Immunology, University of Western Ontario, London, Ontario N6A 5C1, Canada
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24
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Dawson A, Finnegan DJ. Excision of the Drosophila mariner transposon Mos1. Comparison with bacterial transposition and V(D)J recombination. Mol Cell 2003; 11:225-35. [PMID: 12535535 DOI: 10.1016/s1097-2765(02)00798-0] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
It has been proposed that the modern immune system has evolved from a transposon in an ancient vertebrate. While much is known about the mechanism by which bacterial transposable elements catalyze double-strand breaks at their ends, less is known about how eukaryotic transposable elements carry out these reactions. We have examined the mechanism by which mariner, a eukaryotic transposable element, performs DNA cleavage. We show that the nontransferred strand is cleaved initially, unlike prokaryotic transposons which cleave the transferred strand first. First strand cleavage is not tightly coupled to second strand cleavage and can occur independently of synapsis, as happens in V(D)J recombination but not in transposition of prokaryotic transposons. Unlike V(D)J recombination, however, second strand cleavage of mariner does not occur via a hairpin intermediate.
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Affiliation(s)
- Angela Dawson
- Institute of Cell and Molecular Biology, University of Edinburgh, Kings Buildings, Edinburgh EH9 3JR, United Kingdom.
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25
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Izsvák Z, Khare D, Behlke J, Heinemann U, Plasterk RH, Ivics Z. Involvement of a bifunctional, paired-like DNA-binding domain and a transpositional enhancer in Sleeping Beauty transposition. J Biol Chem 2002; 277:34581-8. [PMID: 12082109 DOI: 10.1074/jbc.m204001200] [Citation(s) in RCA: 119] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Sleeping Beauty (SB) is the most active Tc1/mariner-like transposon in vertebrate species. Each of the terminal inverted repeats (IRs) of SB contains two transposase-binding sites (DRs). This feature, termed the IR/DR structure, is conserved in a group of Tc1-like transposons. The DNA-binding region of SB transposase, similar to the paired domain of Pax proteins, consists of two helix-turn-helix subdomains (PAI + RED = PAIRED). The N-terminal PAI subdomain was found to play a dominant role in contacting the DRs. Transposase was able to bind to mutant sites retaining the 3' part of the DRs; thus, primary DNA binding is not sufficient to determine the specificity of the transposition reaction. The PAI subdomain was also found to bind to a transpositional enhancer-like sequence within the left IR of SB, and to mediate protein-protein interactions between transposase subunits. A tetrameric form of the transposase was detected in solution, consistent with an interaction between the IR/DR structure and a transposase tetramer. We propose a model in which the transpositional enhancer and the PAI subdomain stabilize complexes formed by a transposase tetramer bound at the IR/DR. These interactions may result in enhanced stability of synaptic complexes, which might explain the efficient transposition of Sleeping Beauty in vertebrate cells.
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Affiliation(s)
- Zsuzsanna Izsvák
- Max Delbrück Center for Molecular Medicine, Robert Rössle Strasse 10, D-13092 Berlin, Germany
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26
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Loot C, Turlan C, Rousseau P, Ton-Hoang B, Chandler M. A target specificity switch in IS911 transposition: the role of the OrfA protein. EMBO J 2002; 21:4172-82. [PMID: 12145217 PMCID: PMC126149 DOI: 10.1093/emboj/cdf403] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The role played by insertion sequence IS911 proteins, OrfA and OrfAB, in the choice of a target for insertion was studied. IS911 transposition occurs in several steps: synapsis of the two transposon ends (IRR and IRL); formation of a figure-of-eight intermediate where both ends are joined by a single-strand bridge; resolution into a circular form carrying an IRR-IRL junction; and insertion into a DNA target. In vivo, with OrfAB alone, an IS911-based transposon integrated with high probability next to an IS911 end located on the target plasmid. OrfA greatly reduced the proportion of these events. This was confirmed in vitro using a transposon with a preformed IRR-IRL junction to examine the final insertion step. Addition of OrfA resulted in a large increase in insertion frequency and greatly increased the proportion of non-targeted insertions. The intermolecular reaction leading to targeted insertion may resemble the intramolecular reaction involving figure-of-eight molecules, which leads to the formation of circles. OrfA could, therefore, be considered as a molecular switch modulating the site-specific recombination activity of OrfAB and facilitating dispersion of the insertion sequence (IS) to 'non-homologous' target sites.
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Affiliation(s)
| | | | | | | | - M. Chandler
- Laboratoire de Microbiologie et Génétique Moléculaire, CNRS UMR5100, 118 Rte de Narbonne, F-31062 Toulouse Cedex, France
Corresponding author e-mail:
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27
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Abstract
In the first step of IS2 transposition, the formation of an IS2 minicircle, the roles of the two IS ends differ. Terminal cleavage initiates exclusively at the right inverted repeat (IRR) - the donor end - whereas IRL is always the target. At the resulting minicircle junction, the two abutted ends are separated by a spacer of 1 or 2 basepairs. In this study, we have identified the determinants of donor and target function. The inability of IRL to act as a donor results largely from two sequence differences between IRL and IRR - an extra basepair between the conserved transposase binding sequences and the end of the element, and a change of the terminal dinucleotide from CA-3' to TA-3'. These two changes also impose a characteristic size on the minicircle junction spacer. The only sequences required for the efficient target function of IRL appear to be contained within the segment from position 11-42. Although IRR can function as a target, its shorter length and additional contacts with transposase (positions 1-7) result in minicircles with longer, and inappropriate, spacers. We propose a model for the synaptic complex in which the terminus of IRL makes different contacts with the transposase for the initial and final strand transfer steps. The sequence differences between IRR and IRL, and the behavioural characteristics of IRL that result from them, have probably been selected because they optimize expression of transposase from the minicircle junction promoter, Pjunc.
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Affiliation(s)
- L A Lewis
- Department of Biology, York College and Program in Cellular, Molecular and Developmental Biology, Graduate School and University Center, City University of New York, Jamaica, NY 11451, USA.
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28
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Duval-Valentin G, Normand C, Khemici V, Marty B, Chandler M. Transient promoter formation: a new feedback mechanism for regulation of IS911 transposition. EMBO J 2001; 20:5802-11. [PMID: 11598022 PMCID: PMC125674 DOI: 10.1093/emboj/20.20.5802] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
IS911 transposition involves a free circular transposon intermediate where the terminal inverted repeat sequences are connected. Transposase synthesis is usually driven by a weak promoter, p(IRL), in the left end (IRL). Circle junction formation creates a strong promoter, p(junc), with a -35 sequence located in the right end and the -10 sequence in the left. p(junc) assembly would permit an increase in synthesis of transposase from the transposon circle, which would be expected to stimulate integration. Insertion results in p(junc) disassembly and a return to the low p(IRL)- driven transposase levels. We demonstrate that p(junc) plays an important role in regulating IS911 transposition. Inactivation of p(junc) strongly decreased IS911 transposition when transposase was produced in its natural configuration. This novel feedback mechanism permits transient and controlled activation of integration only in the presence of the correct (circular) intermediate. We have also investigated other members of the IS3 and other IS families. Several, but not all, IS3 family members possess p(junc) equivalents, underlining that the regulatory mechanisms adopted to fine-tune transposition may be different.
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Affiliation(s)
| | | | | | | | - Michael Chandler
- Laboratoire de Microbiologie et Génétique Moléculaire, CNRS, 118 Route de Narbonne, 31062 Toulouse, France
Corresponding author e-mail:
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