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Cargo Genes of Tn 7-Like Transposons Comprise an Enormous Diversity of Defense Systems, Mobile Genetic Elements, and Antibiotic Resistance Genes. mBio 2021; 12:e0293821. [PMID: 34872347 PMCID: PMC8649781 DOI: 10.1128/mbio.02938-21] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Transposition is a major mechanism of horizontal gene mobility in prokaryotes. However, exploration of the genes mobilized by transposons (cargo) is hampered by the difficulty in delineating integrated transposons from their surrounding genetic context. Here, we present a computational approach that allowed us to identify the boundaries of 6,549 Tn7-like transposons. We found that 96% of these transposons carry at least one cargo gene. Delineation of distinct communities in a gene-sharing network demonstrates how transposons function as a conduit of genes between phylogenetically distant hosts. Comparative analysis of the cargo genes reveals significant enrichment of mobile genetic elements (MGEs) nested within Tn7-like transposons, such as insertion sequences and toxin-antitoxin modules, and of genes involved in recombination, anti-MGE defense, and antibiotic resistance. More unexpectedly, cargo also includes genes encoding central carbon metabolism enzymes. Twenty-two Tn7-like transposons carry both an anti-MGE defense system and antibiotic resistance genes, illustrating how bacteria can overcome these combined pressures upon acquisition of a single transposon. This work substantially expands the distribution of Tn7-like transposons, defines their evolutionary relationships, and provides a large-scale functional classification of prokaryotic genes mobilized by transposition.
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Mehalko JL, Esposito D. Engineering the transposition-based baculovirus expression vector system for higher efficiency protein production from insect cells. J Biotechnol 2016; 238:1-8. [PMID: 27616621 PMCID: PMC5067234 DOI: 10.1016/j.jbiotec.2016.09.002] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2016] [Revised: 08/26/2016] [Accepted: 09/02/2016] [Indexed: 01/14/2023]
Abstract
One of the most common methods for producing recombinant baculovirus for insect cell protein production involves a transposition mediated system invented over 2 decades ago. This Tn7-mediated system, commercially sold as Bac-to-Bac, has proven highly useful for construction of high quality baculovirus, but suffers from a number of drawbacks which reduce the efficiency of the process and limit its utility for high throughput protein production processes. We describe here the creation of Bac-2-the-Future, a 2nd generation Tn7-based system for recombinant baculovirus production which uses optimized expression vectors, new E. coli strains, and enhanced protocols to dramatically enhance the efficiency of the baculovirus production process. The new system which we describe eliminates the need for additional screening of positive clones, improves the efficiency of transposition, and reduces the cost and time required for high throughput baculovirus production. The system is compatible with multiple cloning methodologies, and has been demonstrated to produce baculovirus with equal or better titer and protein productivity than the currently available systems.
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Affiliation(s)
- Jennifer L Mehalko
- Protein Expression Laboratory, Cancer Research Technology Program, Frederick National Laboratory for Cancer Research, Leidos Biomedical Research, Inc. PO Box B, Frederick, MD 21702, United States
| | - Dominic Esposito
- Protein Expression Laboratory, Cancer Research Technology Program, Frederick National Laboratory for Cancer Research, Leidos Biomedical Research, Inc. PO Box B, Frederick, MD 21702, United States.
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Bustamante P, Tello M, Orellana O. Toxin-antitoxin systems in the mobile genome of Acidithiobacillus ferrooxidans. PLoS One 2014; 9:e112226. [PMID: 25384039 PMCID: PMC4226512 DOI: 10.1371/journal.pone.0112226] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2014] [Accepted: 10/09/2014] [Indexed: 11/18/2022] Open
Abstract
Toxin-antitoxin (TA) systems are genetic modules composed of a pair of genes encoding a stable toxin and an unstable antitoxin that inhibits toxin activity. They are widespread among plasmids and chromosomes of bacteria and archaea. TA systems are known to be involved in the stabilization of plasmids but there is no consensus about the function of chromosomal TA systems. To shed light on the role of chromosomally encoded TA systems we analyzed the distribution and functionality of type II TA systems in the chromosome of two strains from Acidithiobacillus ferrooxidans (ATCC 23270 and 53993), a Gram-negative, acidophilic, environmental bacterium that participates in the bioleaching of minerals. As in other environmental microorganisms, A. ferrooxidans has a high content of TA systems (28-29) and in twenty of them the toxin is a putative ribonuclease. According to the genetic context, some of these systems are encoded near or within mobile genetic elements. Although most TA systems are shared by both strains, four of them, which are encoded in the active mobile element ICEAfe1, are exclusive to the type strain ATCC 23270. We demostrated that two TA systems from ICEAfe1 are functional in E. coli cells, since the toxins inhibit growth and the antitoxins counteract the effect of their cognate toxins. All the toxins from ICEAfe1, including a novel toxin, are RNases with different ion requirements. The data indicate that some of the chromosomally encoded TA systems are actually part of the A. ferrooxidans mobile genome and we propose that could be involved in the maintenance of these integrated mobile genetic elements.
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Affiliation(s)
- Paula Bustamante
- Programa de Biología Celular y Molecular, ICBM, Facultad de Medicina, Universidad de Chile, Santiago, Chile
| | - Mario Tello
- Centro de Biotecnología Acuícola, Departamento de Biología, Facultad de Química y Biología, Universidad de Santiago de Chile, Santiago, Chile
| | - Omar Orellana
- Programa de Biología Celular y Molecular, ICBM, Facultad de Medicina, Universidad de Chile, Santiago, Chile
- * E-mail:
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4
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Abstract
ABSTRACT
The bacterial transposon Tn7 is distinguished by the levels of control it displays over transposition and its capacity to utilize different kinds of target sites. Transposition is carried out using five transposon-encoded proteins, TnsA, TnsB, TnsC, TnsD, and TnsE, which facilitate transfer of the element while minimizing the chances of inactivating host genes by using two pathways of transposition. One of these pathways utilizes TnsD, which targets transposition into a single site found in bacteria (
attTn7
), and a second utilizes TnsE, which preferentially directs transposition into plasmids capable of moving between bacteria. Control of transposition involves a heteromeric transposase that consists of two proteins, TnsA and TnsB, and a regulator protein TnsC. Tn7 also has the ability to inhibit transposition into a region already occupied by the element in a process called target immunity. Considerable information is available about the functional interactions of the Tn7 proteins and many of the protein–DNA complexes involved in transposition. Tn7-like elements that encode homologs of all five of the proteins found in Tn7 are common in diverse bacteria, but a newly appreciated larger family of elements appears to use the same core TnsA, TnsB, and TnsC proteins with other putative target site selector proteins allowing different targeting pathways.
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Lessons from the genomes of extremely acidophilic bacteria and archaea with special emphasis on bioleaching microorganisms. Appl Microbiol Biotechnol 2010; 88:605-20. [DOI: 10.1007/s00253-010-2795-9] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2010] [Revised: 07/22/2010] [Accepted: 07/22/2010] [Indexed: 10/19/2022]
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Mitra R, McKenzie GJ, Yi L, Lee CA, Craig NL. Characterization of the TnsD-attTn7 complex that promotes site-specific insertion of Tn7. Mob DNA 2010; 1:18. [PMID: 20653944 PMCID: PMC2918618 DOI: 10.1186/1759-8753-1-18] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2010] [Accepted: 07/23/2010] [Indexed: 11/10/2022] Open
Abstract
The bacterial transposon Tn7 is distinguished by its ability to recognize a specific site called attTn7, and insert just downstream of the highly conserved chromosomal glmS gene. TnsD is one of four transposon-encoded polypeptides (TnsABC+D) required for site-specific insertion of Tn7 into attTn7, and is the target site-selector that binds to a highly conserved sequence in the end of the glmS protein coding region. In this study, we identified important nucleotides within this region that are crucial for TnsD-attTn7 interaction. We also probed the regions of TnsD that interact with attTn7 and found that there are important DNA-binding determinants throughout the entire length of the protein, including an amino-terminal CCCH zinc-finger motif. A key role of TnsD is to recruit the non-sequence specific DNA-binding protein TnsC to attTn7; TnsC also interacts with and controls both the TnsA and TnsB subunits of the Tn7 transposase. TnsC stimulates the binding of TnsD to attTn7 in vivo, and TnsCD and TnsD can also interact in the absence of DNA and localize their interaction domains to the N-terminal region of each protein.
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Affiliation(s)
- Rupak Mitra
- Howard Hughes Medical Institute, Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore MD 21205, USA
| | - Gregory J McKenzie
- Howard Hughes Medical Institute, Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore MD 21205, USA.,Current Address: Verenium Corporation. 4955 Directors Place, San Diego, CA 92121, USA
| | - Liang Yi
- Howard Hughes Medical Institute, Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore MD 21205, USA.,Current Address: Laboratory of Host Defense, NIAID/NIH, Bethesda, MD 20892, USA
| | - Cherline A Lee
- Howard Hughes Medical Institute, Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore MD 21205, USA.,Current Address: Mayo Clinic, 417 Guggenheim Bldg, 200 First St. SW, Rochester, MN 55905, USA
| | - Nancy L Craig
- Howard Hughes Medical Institute, Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore MD 21205, USA
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Rose A. TnAbaR1: a novel Tn7-related transposon in Acinetobacter baumannii that contributes to the accumulation and dissemination of large repertoires of resistance genes. ACTA ACUST UNITED AC 2010. [DOI: 10.1093/biohorizons/hzq006] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
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Novel insights about class 2 integrons from experimental and genomic epidemiology. Antimicrob Agents Chemother 2009; 54:699-706. [PMID: 19917745 DOI: 10.1128/aac.01392-08] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
In order to contribute to the knowledge of the architecture and epidemiology of class 2 integrons, we performed a class 2 integron molecular survey in which we analyzed 726 isolates in two bacterial populations from environmental and nonepidemiologically related clinical samples, respectively, collected from 1982 to 2007. We recovered the intI2 gene from 130 of 726 isolates, most of which were clinical isolates, and only 1 (a psychrophilic Pseudomonas sp.) was from a water sample. Unlike the widespread distribution of class 1 integrons within Gram-negative bacilli, only Acinetobacter baumannii and Enterobacter cloacae harbored class 2 integrons at a high frequency in our collection. Class 2 integrons with six novel cassette arrays were documented. Characterization of the transposition module of Tn7, the genetic platform in which class 2 integrons have always been reported, showed tns modules with a mosaic genetic structure. A bioinformatic analysis performed with the tns genes present in sequence databases, the finding of intI2 not associated with tns genes, and the genetic examination of novel tns-like genes found in three isolates indicated the possibility of the independent evolution of the two components related to horizontal gene transfer, the class 2 integrons and the Tn7 transposons.
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Suenaga H, Koyama Y, Miyakoshi M, Miyazaki R, Yano H, Sota M, Ohtsubo Y, Tsuda M, Miyazaki K. Novel organization of aromatic degradation pathway genes in a microbial community as revealed by metagenomic analysis. ISME JOURNAL 2009; 3:1335-48. [PMID: 19587775 DOI: 10.1038/ismej.2009.76] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Several types of environmental bacteria that can aerobically degrade various aromatic compounds have been identified. The catabolic genes in these bacteria have generally been found to form operons, which promote efficient and complete degradation. However, little is known about the degradation pathways in bacteria that are difficult to culture in the laboratory. By functionally screening a metagenomic library created from activated sludge, we had earlier identified 91 fosmid clones carrying genes for extradiol dioxygenase (EDO), a key enzyme in the degradation of aromatic compounds. In this study, we analyzed 38 of these fosmids for the presence and organization of novel genes for aromatics degradation. Only two of the metagenomic clones contained complete degradation pathways similar to those found in known aromatic compound-utilizing bacteria. The rest of the clones contained only subsets of the pathway genes, with novel gene arrangements. A circular 36.7-kb DNA form was assembled from the sequences of clones carrying genes belonging to a novel EDO subfamily. This plasmid-like DNA form, designated pSKYE1, possessed genes for DNA replication and stable maintenance as well as a small set of genes for phenol degradation; the encoded enzymes, phenol hydroxylase and EDO, are capable of the detoxification of aromatic compounds. This gene set was found in 20 of the 38 analyzed clones, suggesting that this 'detoxification apparatus' may be widespread in the environment.
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Affiliation(s)
- Hikaru Suenaga
- Institute for Biological Resources and Functions, National Institute of Advanced Industrial Science and Technology, Tsukuba Central 6, Tsukuba, Ibaraki, Japan.
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Valdés J, Pedroso I, Quatrini R, Dodson RJ, Tettelin H, Blake R, Eisen JA, Holmes DS. Acidithiobacillus ferrooxidans metabolism: from genome sequence to industrial applications. BMC Genomics 2008; 9:597. [PMID: 19077236 PMCID: PMC2621215 DOI: 10.1186/1471-2164-9-597] [Citation(s) in RCA: 315] [Impact Index Per Article: 19.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2008] [Accepted: 12/11/2008] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Acidithiobacillus ferrooxidans is a major participant in consortia of microorganisms used for the industrial recovery of copper (bioleaching or biomining). It is a chemolithoautrophic, gamma-proteobacterium using energy from the oxidation of iron- and sulfur-containing minerals for growth. It thrives at extremely low pH (pH 1-2) and fixes both carbon and nitrogen from the atmosphere. It solubilizes copper and other metals from rocks and plays an important role in nutrient and metal biogeochemical cycling in acid environments. The lack of a well-developed system for genetic manipulation has prevented thorough exploration of its physiology. Also, confusion has been caused by prior metabolic models constructed based upon the examination of multiple, and sometimes distantly related, strains of the microorganism. RESULTS The genome of the type strain A. ferrooxidans ATCC 23270 was sequenced and annotated to identify general features and provide a framework for in silico metabolic reconstruction. Earlier models of iron and sulfur oxidation, biofilm formation, quorum sensing, inorganic ion uptake, and amino acid metabolism are confirmed and extended. Initial models are presented for central carbon metabolism, anaerobic metabolism (including sulfur reduction, hydrogen metabolism and nitrogen fixation), stress responses, DNA repair, and metal and toxic compound fluxes. CONCLUSION Bioinformatics analysis provides a valuable platform for gene discovery and functional prediction that helps explain the activity of A. ferrooxidans in industrial bioleaching and its role as a primary producer in acidic environments. An analysis of the genome of the type strain provides a coherent view of its gene content and metabolic potential.
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Affiliation(s)
- Jorge Valdés
- Center for Bioinformatics and Genome Biology, Fundación Ciencia para la Vida, Facultad de Ciencias de la Salud, Universidad Andres Bello, Santiago, Chile.
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Parks AR, Peters JE. Tn7 elements: engendering diversity from chromosomes to episomes. Plasmid 2008; 61:1-14. [PMID: 18951916 DOI: 10.1016/j.plasmid.2008.09.008] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2008] [Revised: 09/24/2008] [Accepted: 09/29/2008] [Indexed: 11/18/2022]
Abstract
The bacterial transposon Tn7 maintains two distinct lifestyles, one in horizontally transferred DNA and the other in bacterial chromosomes. Access to these two DNA pools is mediated by two separate target selection pathways. The proteins involved in these pathways have evolved to specifically activate transposition into their cognate target-sites using entirely different recognition mechanisms, but the same core transposition machinery. In this review we discuss how the molecular mechanisms of Tn7-like elements contribute to their diversification and how they affect the evolution of their host genomes. The analysis of over 50 Tn7-like elements provides insight into the evolution of Tn7 and Tn7 relatives. In addition to the genes required for transposition, Tn7-like elements transport a wide variety of genes that contribute to the success of diverse organisms. We propose that by decisively moving between mobile and stationary DNA pools, Tn7-like elements accumulate a broad range of genetic material, providing a selective advantage for diverse host bacteria.
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Affiliation(s)
- Adam R Parks
- Department of Microbiology, Cornell University, Ithaca, NY 14853, USA
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Parks AR, Peters JE. Transposon Tn7 is widespread in diverse bacteria and forms genomic islands. J Bacteriol 2006; 189:2170-3. [PMID: 17194796 PMCID: PMC1855776 DOI: 10.1128/jb.01536-06] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We find that relatives of the bacterial transposon Tn7 are widespread in disparate environments and phylogenetically diverse species. These elements form functionally diverse genomic islands at the specific site of Tn7 insertion adjacent to glmS. This work presents the first example of genomic island formation by a DDE type transposon.
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Affiliation(s)
- Adam R Parks
- Department of Microbiology, Cornell University, Ithaca, NY 14853, USA
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McCann J, Stabb EV, Millikan DS, Ruby EG. Population dynamics of Vibrio fischeri during infection of Euprymna scolopes. Appl Environ Microbiol 2004; 69:5928-34. [PMID: 14532046 PMCID: PMC201191 DOI: 10.1128/aem.69.10.5928-5934.2003] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The luminous bacterium Vibrio fischeri colonizes a specialized light-emitting organ within its squid host, Euprymna scolopes. Newly hatched juvenile squid must acquire their symbiont from ambient seawater, where the bacteria are present at low concentrations. To understand the population dynamics of V. fischeri during colonization more fully, we used mini-Tn7 transposons to mark bacteria with antibiotic resistance so that the growth of their progeny could be monitored. When grown in culture, there was no detectable metabolic burden on V. fischeri cells carrying the transposon, which inserts in single copy in a specific intergenic region of the V. fischeri genome. Strains marked with mini-Tn7 also appeared to be equivalent to the wild type in their ability to infect and multiply within the host during coinoculation experiments. Studies of the early stages of colonization suggested that only a few bacteria became associated with symbiotic tissue when animals were exposed for a discrete period (3 h) to an inoculum of V. fischeri cells equivalent to natural population levels; nevertheless, all these hosts became infected. When three differentially marked strains of V. fischeri were coincubated with juvenile squid, the number of strains recovered from an individual symbiotic organ was directly dependent on the size of the inoculum. Further, these results indicated that, when exposed to low numbers of V. fischeri, the host may become colonized by only one or a few bacterial cells, suggesting that symbiotic infection is highly efficient.
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Affiliation(s)
- Jessica McCann
- Pacific Biomedical Research Center, University of Hawaii, Honolulu, Hawaii 96813, USA
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Skelding Z, Sarnovsky R, Craig NL. Formation of a nucleoprotein complex containing Tn7 and its target DNA regulates transposition initiation. EMBO J 2002; 21:3494-504. [PMID: 12093750 PMCID: PMC126096 DOI: 10.1093/emboj/cdf347] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Tn7 insertion into its specific target site, attTn7, is mediated by the proteins TnsA, TnsB, TnsC and TnsD. The double-strand breaks that separate Tn7 from the donor DNA require the Tns proteins, the transposon and an attTn7 target DNA, suggesting that a prerequisite for transposition is the formation of a nucleoprotein complex containing TnsABC+D, and these DNAs. Here, we identify a TnsABC+D transposon-attTn7 complex, and demonstrate that it is a transposition intermediate. We demonstrate that an interaction between TnsB, the transposase subunit that binds to the transposon ends, and TnsC, the target DNA-binding protein that controls the activity of the transposase, is essential for assembly of the TnsABC+D transposon-attTn7 complex. We also show that certain TnsB residues are required for recombination because they mediate a TnsB-TnsC interaction critical to formation of the TnsABC+D transposon-attTn7 complex. We demonstrate that TnsA, the other transposase subunit, which also interacts with TnsC, greatly stabilizes the TnsABC+D transposon-attTn7 complex. Thus multiple interactions between the transposase subunits, TnsA and TnsB, and the target-binding transposase activator, TnsC, control Tn7 transposition.
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Affiliation(s)
| | - Robert Sarnovsky
- Howard Hughes Medical Institute, Department of Molecular Biology and Genetics, Johns Hopkins School of Medicine, Baltimore, MD and
National Cancer Institute, Building 37, Room 5124, 37 Convent Drive, MSC 4264, Bethesda, MD 20892-4264, USA Corresponding author e-mail:
| | - Nancy L. Craig
- Howard Hughes Medical Institute, Department of Molecular Biology and Genetics, Johns Hopkins School of Medicine, Baltimore, MD and
National Cancer Institute, Building 37, Room 5124, 37 Convent Drive, MSC 4264, Bethesda, MD 20892-4264, USA Corresponding author e-mail:
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Abstract
A notable feature of transposable elements--segments of DNA that can move from one position to another in genomes--is that they are highly prevalent, despite the fact that their translocation can result in mutation. The bacterial transposon Tn7 uses an elaborate system of target-site selection pathways that favours the dispersal of Tn7 in diverse hosts as well as minimizing its negative effects.
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Affiliation(s)
- J E Peters
- Howard Hughes Medical Institute, Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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16
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Peters JE, Craig NL. Tn7 recognizes transposition target structures associated with DNA replication using the DNA-binding protein TnsE. Genes Dev 2001; 15:737-47. [PMID: 11274058 PMCID: PMC312648 DOI: 10.1101/gad.870201] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
We report that the bacterial transposon Tn7 selects targets by recognizing features associated with DNA replication using the transposon-encoded DNA-binding protein TnsE. We show that Tn7 transposition directed by TnsE occurs in one orientation with respect to chromosomal DNA replication, indicating that a structure or complex involved in DNA replication is likely to be a critical determinant of TnsE insertion. We find that mutant TnsE proteins that allow higher levels of transposition also bind DNA better than the wild-type protein. The increased binding affinity displayed by the TnsE high-activity mutants indicates that DNA binding is relevant to transposition activity and suggests that TnsE interacts directly with target DNAs. In vitro, TnsE interacts preferentially with certain DNA structures, indicating a mechanism for the TnsE-mediated orientation and insertion preference. The pattern of TnsE-mediated insertion events around the Escherichia coli chromosome provides insight into how DNA replication forks proceed in vivo.
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Affiliation(s)
- J E Peters
- Howard Hughes Medical Institute, Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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