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      Multiplexed and portable nucleic acid detection platform with Cas13, Cas12a, and Csm6

      , , , , ,
      Science
      American Association for the Advancement of Science (AAAS)

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          Abstract

          Rapid detection of nucleic acids is integral for clinical diagnostics and biotechnological applications. We recently developed a platform termed SHERLOCK (Specific High Sensitivity Enzymatic Reporter UnLOCKing) that combines isothermal pre-amplification with Cas13 to detect single molecules of RNA or DNA. Through characterization of CRISPR enzymology and application development, we report here four advances integrated into SHERLOCKv2: 1) 4-channel single reaction multiplexing using orthogonal CRISPR enzymes; 2) quantitative measurement of input down to 2 aM; 3) 3.5-fold increase in signal sensitivity by combining Cas13 with Csm6, an auxilary CRISPR-associated enzyme; and 4) lateral flow read-out. SHERLOCKv2 can detect Dengue or Zika virus ssRNA as well as mutations in patient liquid biopsy samples via lateral flow, highlighting its potential as a multiplexable, portable, rapid, and quantitative detection platform of nucleic acids.

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          Most cited references12

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          Discovery and Functional Characterization of Diverse Class 2 CRISPR-Cas Systems.

          Microbial CRISPR-Cas systems are divided into Class 1, with multisubunit effector complexes, and Class 2, with single protein effectors. Currently, only two Class 2 effectors, Cas9 and Cpf1, are known. We describe here three distinct Class 2 CRISPR-Cas systems. The effectors of two of the identified systems, C2c1 and C2c3, contain RuvC-like endonuclease domains distantly related to Cpf1. The third system, C2c2, contains an effector with two predicted HEPN RNase domains. Whereas production of mature CRISPR RNA (crRNA) by C2c1 depends on tracrRNA, C2c2 crRNA maturation is tracrRNA independent. We found that C2c1 systems can mediate DNA interference in a 5'-PAM-dependent fashion analogous to Cpf1. However, unlike Cpf1, which is a single-RNA-guided nuclease, C2c1 depends on both crRNA and tracrRNA for DNA cleavage. Finally, comparative analysis indicates that Class 2 CRISPR-Cas systems evolved on multiple occasions through recombination of Class 1 adaptation modules with effector proteins acquired from distinct mobile elements.
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            Diversity and evolution of class 2 CRISPR–Cas systems

            Class 2 CRISPR–Cas systems are characterized by effector modules that consist of a single multidomain protein. In this Analysis, using a computational pipeline, the authors discover three novel families of class 2 effectors that correspond to three new CRISPR–Cas subtypes and present a comprehensive census of class 2 systems that are encoded in complete and draft bacterial and archaeal genomes.
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              Conditional tolerance of temperate phages via transcription-dependent CRISPR-Cas targeting

              A fundamental feature of immune systems is the ability to distinguish pathogenic from self and commensal elements, and to attack the former but tolerate the latter 1 . Prokaryotic CRISPR-Cas immune systems defend against phage infection using Cas nucleases and small RNA guides that specify one or more target sites for cleavage of the viral genome 2,3 . Temperate phages are viruses that can integrate into the bacterial chromosome, and they can carry genes that provide a fitness advantage to the lysogenic host 4,5 . However, CRISPR-Cas targeting that relies strictly on DNA sequence recognition provides indiscriminate immunity to both lytic and lysogenic infection by temperate phages 6 —compromising the genetic stability of these potentially beneficial elements altogether. Here we show that the Staphylococcus epidermidis CRISPR-Cas system can prevent lytic infection but tolerate lysogenization by temperate phages. Conditional tolerance is achieved through transcription-dependent DNA targeting, and ensures that targeting is resumed upon induction of the prophage lytic cycle. Our results provide evidence for the functional divergence of CRISPR-Cas systems and highlight the importance of targeting mechanism diversity. In addition, they extend the concept of ‘tolerance to non-self’ to the prokaryotic branch of adaptive immunity.
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                Author and article information

                Journal
                Science
                Science
                American Association for the Advancement of Science (AAAS)
                0036-8075
                1095-9203
                April 26 2018
                April 27 2018
                April 27 2018
                February 15 2018
                : 360
                : 6387
                : 439-444
                Article
                10.1126/science.aaq0179
                5961727
                29449508
                715c5470-8aef-4e0e-9cf4-6dd3cc4d88b4
                © 2018

                http://www.sciencemag.org/about/science-licenses-journal-article-reuse

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