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Nickel L, Weidenbach K, Jäger D, Backofen R, Lange SJ, Heidrich N, Schmitz RA. Two CRISPR-Cas systems in Methanosarcina mazei strain Gö1 display common processing features despite belonging to different types I and III. RNA Biol 2013; 10:779-91. [PMID: 23619576 DOI: 10.4161/rna.23928] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The clustered regularly interspaced short palindromic repeats (CRISPR) system represents a highly adaptive and heritable defense system against foreign nucleic acids in bacteria and archaea. We analyzed the two CRISPR-Cas systems in Methanosarcina mazei strain Gö1. Although belonging to different subtypes (I-B and III-B), the leaders and repeats of both loci are nearly identical. Also, despite many point mutations in each array, a common hairpin motif was identified in the repeats by a bioinformatics analysis and in vitro structural probing. The expression and maturation of CRISPR-derived RNAs (crRNAs) were studied in vitro and in vivo. Both respective potential Cas6b-type endonucleases were purified and their activity tested in vitro. Each protein showed significant activity and could cleave both repeats at the same processing site. Cas6b of subtype III-B, however, was significantly more efficient in its cleavage activity compared with Cas6b of subtype I-B. Northern blot and differential RNAseq analyses were performed to investigate in vivo transcription and maturation of crRNAs, revealing generally very low expression of both systems, whereas significant induction at high NaCl concentrations was observed. crRNAs derived proximal to the leader were generally more abundant than distal ones and in vivo processing sites were clarified for both loci, confirming the previously well-established 8 nt 5' repeat tags. The 3'-ends were more diverse, but generally ended in a prefix of the following repeat sequence (3'-tag). The analysis further revealed a 5'-hydroxy and 3'-phosphate termini architecture of small crRNAs specific for cleavage products of Cas6 endonucleases from type I-E and I-F and type III-B.
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Affiliation(s)
- Lisa Nickel
- Institut für Allgemeine Mikrobiologie, Christian-Albrechts-Universität zu Kiel, Am Botanischen Garten 1-9, Kiel, Germany
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152
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Chylinski K, Le Rhun A, Charpentier E. The tracrRNA and Cas9 families of type II CRISPR-Cas immunity systems. RNA Biol 2013; 10:726-37. [PMID: 23563642 PMCID: PMC3737331 DOI: 10.4161/rna.24321] [Citation(s) in RCA: 263] [Impact Index Per Article: 23.9] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
CRISPR-Cas is a rapidly evolving RNA-mediated adaptive immune system that protects bacteria and archaea against mobile genetic elements. The system relies on the activity of short mature CRISPR RNAs (crRNAs) that guide Cas protein(s) to silence invading nucleic acids. A set of CRISPR-Cas, type II, requires a trans-activating small RNA, tracrRNA, for maturation of precursor crRNA (pre-crRNA) and interference with invading sequences. Following co-processing of tracrRNA and pre-crRNA by RNase III, dual-tracrRNA:crRNA guides the CRISPR-associated endonuclease Cas9 (Csn1) to cleave site-specifically cognate target DNA. Here, we screened available genomes for type II CRISPR-Cas loci by searching for Cas9 orthologs. We analyzed 75 representative loci, and for 56 of them we predicted novel tracrRNA orthologs. Our analysis demonstrates a high diversity in cas operon architecture and position of the tracrRNA gene within CRISPR-Cas loci. We observed a correlation between locus heterogeneity and Cas9 sequence diversity, resulting in the identification of various type II CRISPR-Cas subgroups. We validated the expression and co-processing of predicted tracrRNAs and pre-crRNAs by RNA sequencing in five bacterial species. This study reveals tracrRNA family as an atypical, small RNA family with no obvious conservation of structure, sequence or localization within type II CRISPR-Cas loci. The tracrRNA family is however characterized by the conserved feature to base-pair to cognate pre-crRNA repeats, an essential function for crRNA maturation and DNA silencing by dual-RNA:Cas9. The large panel of tracrRNA and Cas9 ortholog sequences should constitute a useful database to improve the design of RNA-programmable Cas9 as genome editing tool.
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Affiliation(s)
- Krzysztof Chylinski
- The Laboratory for Molecular Infection Medicine Sweden (MIMS), Umeå Centre for Microbial Research (UCMR), Department of Molecular Biology, Umeå University, Umeå, Sweden
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153
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Vercoe RB, Chang JT, Dy RL, Taylor C, Gristwood T, Clulow JS, Richter C, Przybilski R, Pitman AR, Fineran PC. Cytotoxic chromosomal targeting by CRISPR/Cas systems can reshape bacterial genomes and expel or remodel pathogenicity islands. PLoS Genet 2013; 9:e1003454. [PMID: 23637624 PMCID: PMC3630108 DOI: 10.1371/journal.pgen.1003454] [Citation(s) in RCA: 256] [Impact Index Per Article: 23.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2012] [Accepted: 03/02/2013] [Indexed: 12/26/2022] Open
Abstract
In prokaryotes, clustered regularly interspaced short palindromic repeats (CRISPRs) and their associated (Cas) proteins constitute a defence system against bacteriophages and plasmids. CRISPR/Cas systems acquire short spacer sequences from foreign genetic elements and incorporate these into their CRISPR arrays, generating a memory of past invaders. Defence is provided by short non-coding RNAs that guide Cas proteins to cleave complementary nucleic acids. While most spacers are acquired from phages and plasmids, there are examples of spacers that match genes elsewhere in the host bacterial chromosome. In Pectobacterium atrosepticum the type I-F CRISPR/Cas system has acquired a self-complementary spacer that perfectly matches a protospacer target in a horizontally acquired island (HAI2) involved in plant pathogenicity. Given the paucity of experimental data about CRISPR/Cas-mediated chromosomal targeting, we examined this process by developing a tightly controlled system. Chromosomal targeting was highly toxic via targeting of DNA and resulted in growth inhibition and cellular filamentation. The toxic phenotype was avoided by mutations in the cas operon, the CRISPR repeats, the protospacer target, and protospacer-adjacent motif (PAM) beside the target. Indeed, the natural self-targeting spacer was non-toxic due to a single nucleotide mutation adjacent to the target in the PAM sequence. Furthermore, we show that chromosomal targeting can result in large-scale genomic alterations, including the remodelling or deletion of entire pre-existing pathogenicity islands. These features can be engineered for the targeted deletion of large regions of bacterial chromosomes. In conclusion, in DNA-targeting CRISPR/Cas systems, chromosomal interference is deleterious by causing DNA damage and providing a strong selective pressure for genome alterations, which may have consequences for bacterial evolution and pathogenicity.
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Affiliation(s)
- Reuben B. Vercoe
- Department of Microbiology and Immunology, University of Otago, Dunedin, New Zealand
| | - James T. Chang
- Department of Microbiology and Immunology, University of Otago, Dunedin, New Zealand
| | - Ron L. Dy
- Department of Microbiology and Immunology, University of Otago, Dunedin, New Zealand
| | - Corinda Taylor
- Department of Microbiology and Immunology, University of Otago, Dunedin, New Zealand
| | - Tamzin Gristwood
- Department of Microbiology and Immunology, University of Otago, Dunedin, New Zealand
| | - James S. Clulow
- Department of Microbiology and Immunology, University of Otago, Dunedin, New Zealand
| | - Corinna Richter
- Department of Microbiology and Immunology, University of Otago, Dunedin, New Zealand
| | - Rita Przybilski
- Department of Microbiology and Immunology, University of Otago, Dunedin, New Zealand
| | - Andrew R. Pitman
- New Zealand Institute for Plant and Food Research, Christchurch, New Zealand
- Bio-Protection Research Centre, Lincoln University, Canterbury, New Zealand
| | - Peter C. Fineran
- Department of Microbiology and Immunology, University of Otago, Dunedin, New Zealand
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154
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Elmore JR, Yokooji Y, Sato T, Olson S, Glover CVC, Graveley BR, Atomi H, Terns RM, Terns MP. Programmable plasmid interference by the CRISPR-Cas system in Thermococcus kodakarensis. RNA Biol 2013; 10:828-40. [PMID: 23535213 PMCID: PMC3737340 DOI: 10.4161/rna.24084] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
CRISPR-Cas systems are RNA-guided immune systems that protect prokaryotes against viruses and other invaders. The CRISPR locus encodes crRNAs that recognize invading nucleic acid sequences and trigger silencing by the associated Cas proteins. There are multiple CRISPR-Cas systems with distinct compositions and mechanistic processes. Thermococcus kodakarensis (Tko) is a hyperthermophilic euryarchaeon that has both a Type I-A Csa and a Type I-B Cst CRISPR-Cas system. We have analyzed the expression and composition of crRNAs from the three CRISPRs in Tko by RNA deep sequencing and northern analysis. Our results indicate that crRNAs associated with these two CRISPR-Cas systems include an 8-nucleotide conserved sequence tag at the 5' end. We challenged Tko with plasmid invaders containing sequences targeted by endogenous crRNAs and observed active CRISPR-Cas-mediated silencing. Plasmid silencing was dependent on complementarity with a crRNA as well as on a sequence element found immediately adjacent to the crRNA recognition site in the target termed the PAM (protospacer adjacent motif). Silencing occurred independently of the orientation of the target sequence in the plasmid, and appears to occur at the DNA level, presumably via DNA degradation. In addition, we have directed silencing of an invader plasmid by genetically engineering the chromosomal CRISPR locus to express customized crRNAs directed against the plasmid. Our results support CRISPR engineering as a feasible approach to develop prokaryotic strains that are resistant to infection for use in industry.
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Affiliation(s)
- Joshua R Elmore
- Department of Molecular Biology and Biochemistry, University of Georgia, Athens, GA, USA
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155
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Barrangou R. CRISPR-Cas systems and RNA-guided interference. WILEY INTERDISCIPLINARY REVIEWS-RNA 2013; 4:267-78. [DOI: 10.1002/wrna.1159] [Citation(s) in RCA: 137] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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156
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Makarova KS, Wolf YI, Koonin EV. Comparative genomics of defense systems in archaea and bacteria. Nucleic Acids Res 2013; 41:4360-77. [PMID: 23470997 PMCID: PMC3632139 DOI: 10.1093/nar/gkt157] [Citation(s) in RCA: 297] [Impact Index Per Article: 27.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Our knowledge of prokaryotic defense systems has vastly expanded as the result of comparative genomic analysis, followed by experimental validation. This expansion is both quantitative, including the discovery of diverse new examples of known types of defense systems, such as restriction-modification or toxin-antitoxin systems, and qualitative, including the discovery of fundamentally new defense mechanisms, such as the CRISPR-Cas immunity system. Large-scale statistical analysis reveals that the distribution of different defense systems in bacterial and archaeal taxa is non-uniform, with four groups of organisms distinguishable with respect to the overall abundance and the balance between specific types of defense systems. The genes encoding defense system components in bacterial and archaea typically cluster in defense islands. In addition to genes encoding known defense systems, these islands contain numerous uncharacterized genes, which are candidates for new types of defense systems. The tight association of the genes encoding immunity systems and dormancy- or cell death-inducing defense systems in prokaryotic genomes suggests that these two major types of defense are functionally coupled, providing for effective protection at the population level.
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Affiliation(s)
- Kira S Makarova
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894, USA
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157
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Koonin EV, Makarova KS. CRISPR-Cas: evolution of an RNA-based adaptive immunity system in prokaryotes. RNA Biol 2013; 10:679-86. [PMID: 23439366 DOI: 10.4161/rna.24022] [Citation(s) in RCA: 128] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The CRISPR-Cas (clustered regularly interspaced short palindromic repeats, CRISPR-associated genes) is an adaptive immunity system in bacteria and archaea that functions via a distinct self-non-self recognition mechanism that is partially analogous to the mechanism of eukaryotic RNA interference (RNAi). The CRISPR-Cas system incorporates fragments of virus or plasmid DNA into the CRISPR repeat cassettes and employs the processed transcripts of these spacers as guide RNAs to cleave the cognate foreign DNA or RNA. The Cas proteins, however, are not homologous to the proteins involved in RNAi and comprise numerous, highly diverged families. The majority of the Cas proteins contain diverse variants of the RNA recognition motif (RRM), a widespread RNA-binding domain. Despite the fast evolution that is typical of the cas genes, the presence of diverse versions of the RRM in most Cas proteins provides for a simple scenario for the evolution of the three distinct types of CRISPR-cas systems. In addition to several proteins that are directly implicated in the immune response, the cas genes encode a variety of proteins that are homologous to prokaryotic toxins that typically possess nuclease activity. The predicted toxins associated with CRISPR-Cas systems include the essential Cas2 protein, proteins of COG1517 that, in addition to a ligand-binding domain and a helix-turn-helix domain, typically contain different nuclease domains and several other predicted nucleases. The tight association of the CRISPR-Cas immunity systems with predicted toxins that, upon activation, would induce dormancy or cell death suggests that adaptive immunity and dormancy/suicide response are functionally coupled. Such coupling could manifest in the persistence state being induced and potentially providing conditions for more effective action of the immune system or in cell death being triggered when immunity fails.
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Affiliation(s)
- Eugene V Koonin
- National Center for Biotechnology Information, NLM, National Institutes of Health, Bethesda, MD, USA.
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