• Phylogeny of Cas9 determines functional exchangeability of dual-RNA and Cas9 among orthologous type II CRISPR-Cas systems.

      Fonfara, Ines; Le Rhun, Anaïs; Chylinski, Krzysztof; Makarova, Kira S; Lécrivain, Anne-Laure; Bzdrenga, Janek; Koonin, Eugene V; Charpentier, Emmanuelle; The Laboratory for Molecular Infection Medicine Sweden (MIMS), Umeå Centre for Microbial Research (UCMR), Department of Molecular Biology, Umeå University, Umeå S-90187, Sweden, Helmholtz Centre for Infection Research, Department of Regulation in Infection Biology, Braunschweig D-38124, Germany, Deptartment of Biochemistry and Cell Biology, Max F. Perutz Laboratories, University of Vienna, Vienna A-1030, Austria, National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894, USA and Hannover Medical School, Hannover D-30625, Germany. (2013-11-22)
      The CRISPR-Cas-derived RNA-guided Cas9 endonuclease is the key element of an emerging promising technology for genome engineering in a broad range of cells and organisms. The DNA-targeting mechanism of the type II CRISPR-Cas system involves maturation of tracrRNA:crRNA duplex (dual-RNA), which directs Cas9 to cleave invading DNA in a sequence-specific manner, dependent on the presence of a Protospacer Adjacent Motif (PAM) on the target. We show that evolution of dual-RNA and Cas9 in bacteria produced remarkable sequence diversity. We selected eight representatives of phylogenetically defined type II CRISPR-Cas groups to analyze possible coevolution of Cas9 and dual-RNA. We demonstrate that these two components are interchangeable only between closely related type II systems when the PAM sequence is adjusted to the investigated Cas9 protein. Comparison of the taxonomy of bacterial species that harbor type II CRISPR-Cas systems with the Cas9 phylogeny corroborates horizontal transfer of the CRISPR-Cas loci. The reported collection of dual-RNA:Cas9 with associated PAMs expands the possibilities for multiplex genome editing and could provide means to improve the specificity of the RNA-programmable Cas9 tool.
    • RNA sequencing uncovers antisense RNAs and novel small RNAs in Streptococcus pyogenes.

      Le Rhun, Anaïs; Beer, Yan Yan; Reimegård, Johan; Chylinski, Krzysztof; Charpentier, Emmanuelle; Helmholtz Centre for infection research, Inhoffenstr. 7, 38124 Braunschweig, Germany. (2016-02)
      Streptococcus pyogenes is a human pathogen responsible for a wide spectrum of diseases ranging from mild to life-threatening infections. During the infectious process, the temporal and spatial expression of pathogenicity factors is tightly controlled by a complex network of protein and RNA regulators acting in response to various environmental signals. Here, we focus on the class of small RNA regulators (sRNAs) and present the first complete analysis of sRNA sequencing data in S. pyogenes. In the SF370 clinical isolate (M1 serotype), we identified 197 and 428 putative regulatory RNAs by visual inspection and bioinformatics screening of the sequencing data, respectively. Only 35 from the 197 candidates identified by visual screening were assigned a predicted function (T-boxes, ribosomal protein leaders, characterized riboswitches or sRNAs), indicating how little is known about sRNA regulation in S. pyogenes. By comparing our list of predicted sRNAs with previous S. pyogenes sRNA screens using bioinformatics or microarrays, 92 novel sRNAs were revealed, including antisense RNAs that are for the first time shown to be expressed in this pathogen. We experimentally validated the expression of 30 novel sRNAs and antisense RNAs. We show that the expression profile of 9 sRNAs including 2 predicted regulatory elements is affected by the endoribonucleases RNase III and/or RNase Y, highlighting the critical role of these enzymes in sRNA regulation.
    • Toward Whole-Transcriptome Editing with CRISPR-Cas9.

      Heckl, Dirk; Charpentier, Emmanuelle; Helmholtz Centre for infection research, Inhoffenstr. 7, 38124 Braunschweig, Germany. (2015-05-21)
      Targeted regulation of gene expression holds huge promise for biomedical research. In a series of recent publications (Gilbert et al., 2014; Konermann et al., 2015; Zalatan et al., 2015), sophisticated, multiplex-compatible transcriptional activator systems based on the CRISPR-Cas9 technology and genome-scale libraries advance the field toward whole-transcriptome control.
    • The tracrRNA and Cas9 families of type II CRISPR-Cas immunity systems.

      Chylinski, Krzysztof; Le Rhun, Anaïs; Charpentier, Emmanuelle; The Laboratory for Molecular Infection Medicine Sweden (MIMS), Umeå Centre for Microbial Research (UCMR), Department of Molecular Biology, Umeå University, Umeå, Sweden. (2013-05)
      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.
    • A Two-Component Regulatory System Impacts Extracellular Membrane-Derived Vesicle Production in Group A Streptococcus.

      Resch, Ulrike; Tsatsaronis, James Anthony; Le Rhun, Anaïs; Stübiger, Gerald; Rohde, M; Kasvandik, Sergo; Holzmeister, Susanne; Tinnefeld, Philip; Wai, Sun Nyunt; Charpentier, Emmanuelle; et al. (2016)
      Export of macromolecules via extracellular membrane-derived vesicles (MVs) plays an important role in the biology of Gram-negative bacteria. Gram-positive bacteria have also recently been reported to produce MVs; however, the composition and mechanisms governing vesiculogenesis in Gram-positive bacteria remain undefined. Here, we describe MV production in the Gram-positive human pathogen group A streptococcus (GAS), the etiological agent of necrotizing fasciitis and streptococcal toxic shock syndrome. M1 serotype GAS isolates in culture exhibit MV structures both on the cell wall surface and in the near vicinity of bacterial cells. A comprehensive analysis of MV proteins identified both virulence-associated protein substrates of the general secretory pathway in addition to "anchorless surface proteins." Characteristic differences in the contents, distributions, and fatty acid compositions of specific lipids between MVs and GAS cell membrane were also observed. Furthermore, deep RNA sequencing of vesicular RNAs revealed that GAS MVs contained differentially abundant RNA species relative to bacterial cellular RNA. MV production by GAS strains varied in a manner dependent on an intact two-component system, CovRS, with MV production negatively regulated by the system. Modulation of MV production through CovRS was found to be independent of both GAS cysteine protease SpeB and capsule biosynthesis. Our data provide an explanation for GAS secretion of macromolecules, including RNAs, lipids, and proteins, and illustrate a regulatory mechanism coordinating this secretory response.