Patent Publication Number: US-2021166783-A1

Title: Methods for identifying class 2 crispr-cas systems

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 62/376,387 filed Aug. 17, 2016, which is incorporated herein by reference in its entirety. 
    
    
     STATEMENT AS TO FEDERALLY SPONSORED RESEARCH 
     This invention was made with government support under grant numbers MH100706 and MH110049 awarded by the National Institutes of Health. The government has certain rights in the invention. 
    
    
     BACKGROUND 
     The CRISPR-Cas systems embody adaptive immunity in archaea and bacteria. Similar to other defense mechanisms, CRISPR-Cas systems apparently evolve in the regime of incessant arms race with mobile genetic elements which results in extreme diversification of the Cas protein sequences and the architecture of the CRISPR-cas loci. Due to this diversity and the lack of universal cas genes, a comprehensive classification of the CRISPR-Cas systems cannot be generated in the form of a single phylogenetic tree but rather requires a multipronged approach combining identification of signature genes, trees and sequence similarity analysis for partially conserved cas genes, and quantitative comparison of the loci organization. The latest published CRISPR-Cas classification includes two classes that are subdivided into 5 types and 16 subtypes. The CRISPR-Cas systems are characterized by pronounced functional and evolutionary modularity. The module responsible for the first, adaptation step of the CRISPR response, i.e. spacer acquisition, shows limited variation among the diverse variants of CRISPR-Cas systems and consists of the essential cas1 and cas2 genes, often accompanied by the cas4 gene; in some variants, the cas2 gene is fused to cas3. By contrast, the CRISPR-Cas effector module involved in the maturation of the crRNAs as well as target recognition and cleavage, shows a far greater versatility in terms of the gene composition and locus architecture. 
     The two classes of CRISPR-Cas systems have been delineated on the basis of their fundamentally different organizations of the effector modules. The effector complexes of Class 1 systems (Types I, III and IV) consist of four to seven Cas protein subunits in an uneven stoichiometry as exemplified by the CRISPR-associated complex for antiviral defense (Cascade) of the Type I systems, and the Csm/Cmr complexes of the Type III systems. The majority of the subunits of the Class 1 effector complexes, in particular Cas5, Cas6 and Cas7, belong to the so-called RAMP (Repeat-Associated Mysterious Proteins) family of proteins containing the RNA-binding RRM (RNA Recognition Motif) domain. Although it is difficult to detect sequence similarity between individual subunits of Type I and Type III effector complexes, these complexes share similar overall architectures and probably evolved from a common ancestor. 
     The Class 1 systems are most common in bacteria and especially archaea, including all hyperthermophiles, and comprise about 90% of all identified CRISPR-Cas loci. The remaining 10% of the CRISPR-Cas systems belong to Class 2 (Types II and V) that are found almost exclusively in bacteria and never in hyperthermophiles. The signature feature of Class 2 systems is an effector module consisting of a single, multidomain protein. The relative architectural simplicity of the effector complex has made Class 2 CRISPR-cas systems the obvious choice for the new generation of genome-editing tools. The most common and best studied Class 2 effector is Cas9 (Type II), a CRISPR (cr) RNA-dependent endonuclease containing two unrelated nuclease domains, RuvC and HNH, which are responsible for the cleavage of the displaced (non-target) and target DNA strands, respectively, in the crRNA-target DNA complex. The Type II loci also encode a trans-acting CRISPR (tracr)RNA, a derivative of the corresponding CRISPR that is directly involved for pre-crRNA processing and target recognition in Type II systems. 
     The Cpf1 protein, the prototype Type V effector, contains only one readily detectable nuclease domain, RuvC. However, the structures of Cpf1 complexed with the crRNA or with both crRNA and target DNA reveal a second nuclease domain with a unique fold that, however, is functionally analogous to the HNH domain of Cas9, being inserted into the RuvC domain and responsible for the target strand cleavage. Remarkably, Cpf1 differs from Cas9 in that it is a single RNA-guided nuclease that does not require tracrRNA. 
     The discovery of two, distantly related Class 2 effector proteins, Cas9 and Cpf1, suggests that other, distinct variants of such systems could exist. We developed a computational pipeline to systematically identify novel Class 2 CRISPR-Cas loci in genomic and metagenomics sequences. Using Cas1, the most conserved Cas protein, as a seed, we identified 3 previously unknown Class 2 subtypes two of which contained effectors distantly related to Cpf1 and accordingly were included as additional subtypes in type V whereas the third one became the new type VI. The expression and interference activity of two of these proteins, denoted C2c1 and C2c2, has been experimentally demonstrated. 
     SUMMARY 
     We extended the search for novel Class 2 systems by using the CRISPR array itself as the seed, which yielded at least three new CRISPR-Cas subtypes. 
     At least one aspect of invention described herein relates to a method of identifying novel CRISPR effectors, comprising: a) identifying sequences in a genomic or metagenomic database encoding a CRISPR array; b) identifying one or more Open Reading Frames (ORFs) in said selected sequences within 10 kb of the CRISPR array; c) discarding all loci encoding proteins which are assigned to known CRISPR-Cas subtypes and, optionally, all loci encoding a protein of less than 700 amino acids; and d) identifying putative novel CRISPR effectors, and optionally classifying them based on structure analysis. 
     At least another aspect of invention described herein relates to a method for identifying putative CRISPR effectors comprising (a) identifying multiple CRISPR motifs using genome sequencing data; (b) extracting multiple features from said identified CRISPR motifs, such as protein elements, repeat structure, repeat sequence, spacer sequence and spacer mapping; (c) classifying CRISPR loci based on these features using unsupervised learning; (d) identifying conserved locus elements; and (e) selecting therefrom putative CRISPR effector based on structure analysis. 
     At least a further aspect of invention described herein relates to a method of identifying a Class 2 CRISPR effector, comprising: a) comparing sequences in a genomic and/or metagenomic database with at least one pre-identified seed sequence that encodes a CRISPR array, and selecting sequences comprising said seed sequence; b) identifying one or more Open Reading Frames (ORFs) in said selected sequences within 10 kb of the CRISPR array, wherein the ORF encode a protein of at least 300 amino acids and comprising one or more RuvC, HPN, and/or HEPN domains; and c) identifying putative novel CRISPR effectors, and optionally classifying them based on structure analysis. 
     At least an additional aspect of invention described herein relates to a recombinant nucleic acid comprising a nucleic acid sequence encoding a Class 2 CRISPR effector operably linked to a heterologous promoter, wherein the Class 2 CRISPR effector is not Cas9, Cpf1, C2c1, C2c2, C2c3, and C2c6. 
     Yet another aspect of invention described herein relates to an expression cassette comprising the recombinant nucleic acid. Yet a further aspect of invention described herein relates to a vector comprising the expression cassette. Yet an additional aspect of invention described herein relates to a cell transformed with the vector. 
     These and other features, together with the organization and manner of operation thereof, will become apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a computational pipeline for the discovery of Class 2 CRISPR-Cas loci. The procedure begins with the identification of a ‘seed’ that signifies the likely presence of a CRISPR-Cas locus in a given nucleotide sequence. Previously, Cas1 was used as the seed. The Cas protein is most common in CRISPR-Cas systems and is most highly conserved at the sequence level. Here we update this part of the analysis by searching the current sequence databases. To ensure the maximum sensitivity of detection, the search was performed by comparing a Cas1 sequence profile to translated genomic and metagenomic sequences. After the cast genes were detected, the respective neighborhoods were examined for the presence of other cas genes by searching with approximately 400 previously developed profiles for Cas proteins and applying the criteria for the classification of the CRISPR-cas loci. In a complementary approach, to extend the search to non-autonomous CRISPR-Cas systems, the same procedures were repeated with the CRISPR array used as the seed. To ensure high sensitivity of the CRISPR array detection, the union of the predictions made using the PilerCR and CRISPRfinder methods was taken as the final CRISPR set. All loci that were assigned to known CRISPR-Cas subtypes through the Cas protein profile search were discarded from the subsequent analysis given that the search specifically aimed at the discovery of new subtypes. Among the remaining cas1 and CRISPR neighborhoods, those encoding large proteins (&gt;500 amino acids) were chosen for detailed analysis given that Cas9 and Cpf1 are large proteins (typically, &gt;1000 aa), and the respective protein structures suggest that this large size may be required to accommodate the complex of the crRNA with the target DNA. The sequences of such large proteins were then screened for known protein domains using sensitive profile-based methods such as HHpred, secondary structure prediction and manual examination of multiple alignments. Under the premise that Class 2 effector proteins contain nuclease domains, even if in some cases distantly related or unrelated to the known families of nucleases, the proteins containing domains deemed irrelevant in the context of the CRISPR-Cas function (e.g. membrane transporters or metabolic enzymes) were discarded. The retained proteins either contained readily identifiable nuclease domain or were complete unknowns. The sequences of these proteins were then analyzed using the most sensitive current methods for domain detection such as HHPred with a curated multiple alignment of the respective protein sequences used as the query. The use of maximally sensitive methods at this stage is essential because proteins involved in antivirus defense and the Cas proteins in particular typically evolve extremely fast. Note that the depicted procedure for discovery of Class 2 CRISPR-Cas systems, at least in principle, is expected to be exhaustive because all loci containing a gene encoding a large protein (that is, a putative Class 2 effector) in the vicinity of cas1 and/or CRISPR are analyzed in detail. The assumption on the structural requirements for a Class 2 effector underlying the protein size cutoff and the precision of cas1 and CRISPR detection are the only limitations of this approach. 
         FIG. 2  shows a classification scheme for Class 2 CRISPR-cas systems. The Class 1 systems are collapsed. New Class 2 systems discovered using our computational pipeline (see  FIG. 1 ) are shown by blue circles for those described previously or by red circles for those presented here for the first time. For each Class 2 subtype as well as 5 distinct variants of the provisional subtype V-U, the locus organization and the domain architecture organization of the effector proteins are schematically shown. For subtype VI-A, cas1 and cas2 are shown with dashed contours to indicate that only some of these loci include the adaptation module. For the V-U5 variant, the inactivation of the RuvC-like nucleases domain is indicated by a cross. RuvC I, II, III are the three distinct motifs that contribute to the nuclease catalytic center. TM, putative transmembrane helix. The putative target is indicated for each subtype. 
         FIG. 3  shows domain architectures of the Class 2 CRISPR effector proteins. For the type II and subtype V-A effectors, the crystal structures (indicated by the Protein Databank (pdb) accession numbers) are available and accordingly the domain architectures are shown in detail. For the rest of the proteins, the grey areas indicate structurally and functionally uncharacterized portions of the proteins. RuvC I,II,III and HEPN I, II denote the respective catalytic motifs of the nuclease domains of the CRISPR effectors. The proteins are shown to scale. For each protein, the number of amino acids is indicated, and a ruler is shown on top of the figure to guide the eye. For the functionally characterized, full length effectors, the proposed new nomenclature (Cas12 and Cas13) is indicated where as for the putative effectors of type V-U, only the ‘candidate’, provisional names are shown. The asterisks at C2c5 indicates that this putative effector protein contains replacements of the catalytic residues of the RuvC-like nuclease domain and lacks the Zn-finger. 
         FIG. 4  shows phylogenetic tree of TnpB nucleases including type V-U effectors. The major families of TnpB proteins are collapsed and shown by blue triangles. The 4 distinct groups of CRISPR-associated TnpB homologs (putative subtype V-U effectors) are shown by red triangles and blown up to the species level resolution on the right. For these subtrees, bootstrap values (%) are shown at each internal branch. The V-B5 variant is provisionally added at the root of the tree. The presence of a CRISPR array next to the gene encoding a TnpB homolog is indicated for each locus. For the accession number of all sequences included in the tree. 
         FIG. 5  shows phylogenetic tree of the subtype VI-B effector proteins, Cas13b. The tree was constructed as in  FIG. 4 , and the bootstrap values are indicated for each internal branch. The organization of each locus is schematically shown on the right, and the number of CRISPR units is indicated. TPR, tetratricopeptide repeats; WYL, putative ligand-binding domain associated with some CRISPR-Cas systems (named for the 3 conserved amino acid residues); CHASE, cyclase/histidine kinase-associated sensing extracellular domain 
         FIG. 6  shows phylogenies of the type V and type VI-B effectors. (A) Phylogenetic tree of TnpB nucleases including type V-U effectors with a putative active RuvC domain. The major subtrees of TnpB proteins are collapsed and shown by light blue triangles if they include representatives located next to a CRISPR array or by light yellow if no such representatives were identified in the respective branch. Dominant bacterial or archaeal lineages (if any) are indicated in the triangles. Abbreviations: A—diverse archaea; B, diverse bacteria. The 4 distinct groups of CRISPR-associated TnpB homologs (putative subtype V-U effectors) are shown by red triangles; for each of these, the classification and a list of major lineages is provided to the right of the tree. For these subtrees, bootstrap values (%) are shown for selected branches. (B) Phylogenetic tree of the subtype VI-B effector proteins, Cas13b. The tree was constructed as in (A), and the bootstrap values are indicated for selected internal branches. The organization of a typical cas13b locus for selected representatives (bold) is schematically shown on the right. 
         FIG. 7  shows evolutionary scenarios for Class 2 CRISPR-Cas systems. The figure depicts the path of ‘maturation’ of type II and type V systems that starts with random insertion of a TnpB encoding transposon next to a CRISPR cassette and a parallel path for type VI systems initiated by the insertion of a gene encoding a HEPN domain-containing protein, possibly a toxin. 
         FIG. 8  shows functional diversity of the experimentally characterized Class 2 CRISPR-Cas systems. 
         FIG. 9  shows multiple alignment of representatives from five V-U families. V-U1 and V-U4 families are aligned with regular TnpB, whose sequence IDs are shown in bold font. RuvC catalytic residues are highlighted by red letters. 
     
    
    
     DETAILED DESCRIPTION 
     Introduction 
     With respect to general information on CRISPR-Cas Systems, components thereof, and delivery of such components, including methods, materials, delivery vehicles, vectors, particles, AAV, and making and using thereof, including as to amounts and formulations, all useful in the practice of the instant invention, reference is made to: U.S. Pat. Nos. 8,999,641, 8,993,233, 8,945,839, 8,932,814, 8,906,616, 8,895,308, 8,889,418, 8,889,356, 8,871,445, 8,865,406, 8,795,965, 8,771,945 and 8,697,359; US Patent Publications US 2014-0310830 (U.S. application Ser. No. 14/105,031), US 2014-0287938 A1 (U.S. application Ser. No. 14/213,991), US 2014-0273234 A1 (U.S. application Ser. No. 14/293,674), US2014-0273232 A1 (U.S. application Ser. No. 14/290,575), US 2014-0273231 (U.S. application Ser. No. 14/259,420), US 2014-0256046 A1 (U.S. application Ser. No. 14/226,274), US 2014-0248702 A1 (U.S. application Ser. No. 14/258,458), US 2014-0242700 A1 (U.S. application Ser. No. 14/222,930), US 2014-0242699 A1 (U.S. application Ser. No. 14/183,512), US 2014-0242664 A1 (U.S. application Ser. No. 14/104,990), US 2014-0234972 A1 (U.S. application Ser. No. 14/183,471), US 2014-0227787 A1 (U.S. application Ser. No. 14/256,912), US 2014-0189896 A1 (U.S. application Ser. No. 14/105,035), US 2014-0186958 (U.S. application Ser. No. 14/105,017), US 2014-0186919 A1 (U.S. application Ser. No. 14/104,977), US 2014-0186843 A1 (U.S. application Ser. No. 14/104,900), US 2014-0179770 A1 (U.S. application Ser. No. 14/104,837) and US 2014-0179006 A1 (U.S. application Ser. No. 14/183,486), US 2014-0170753 (U.S. application Ser. No. 14/183,429); European Patents EP 2 784 162 B 1 and EP 2 771 468 B 1; European Patent Applications EP 2 771 468 (EP13818570.7), EP 2 764 103 (EP13824232.6), and EP 2 784 162 (EP14170383.5); and PCT Patent Publications PCT Patent Publications WO 2014/093661 (PCT/US2013/074743), WO 2014/093694 (PCT/US2013/074790), WO 2014/093595 (PCT/US2013/074611), WO 2014/093718 (PCT/US2013/074825), WO 2014/093709 (PCT/US2013/074812), WO 2014/093622 (PCT/US2013/074667), WO 2014/093635 (PCT/US2013/074691), WO 2014/093655 (PCT/US2013/074736), WO 2014/093712 (PCT/US2013/074819), WO2014/093701 (PCT/US2013/074800), WO2014/018423 (PCT/US2013/051418), WO 2014/204723 (PCT/US2014/041790), WO 2014/204724 (PCT/US2014/041800), WO 2014/204725 (PCT/US2014/041803), WO 2014/204726 (PCT/US2014/041804), WO 2014/204727 (PCT/US2014/041806), WO 2014/204728 (PCT/US2014/041808), WO 2014/204729 (PCT/US2014/041809). Reference is also made to U.S. provisional patent applications 61/758,468; 61/802,174; 61/806,375; 61/814,263; 61/819,803 and 61/828,130, filed on Jan. 30, 2013; Mar. 15, 2013; Mar. 28, 2013; Apr. 20, 2013; May 6, 2013 and May 28, 2013 respectively. Reference is also made to U.S. provisional patent application 61/836,123, filed on Jun. 17, 2013. Reference is additionally made to U.S. provisional patent applications 61/835,931, 61/835,936, 61/836,127, 61/836, 101, 61/836,080 and 61/835,973, each filed Jun. 17, 2013. Further reference is made to U.S. provisional patent applications 61/862,468 and 61/862,355 filed on Aug. 5, 2013; 61/871,301 filed on Aug. 28, 2013; 61/960,777 filed on Sep. 25, 2013 and 61/961,980 filed on Oct. 28, 2013. Reference is yet further made to: PCT Patent applications Nos: PCT/US2014/041803, PCT/US2014/041800, PCT/US2014/041809, PCT/US2014/041804 and PCT/US2014/041806, each filed Jun. 10, 2014 6/10/14; PCT/US2014/041808 filed Jun. 11, 2014; and PCT/US2014/62558 filed Oct. 28, 2014, and U.S. Provisional Patent Applications Ser. Nos. 61/915,150, 61/915,301, 61/915,267 and 61/915,260, each filed Dec. 12, 2013; 61/757,972 and 61/768,959, filed on Jan. 29, 2013 and Feb. 25, 2013; 61/835,936, 61/836,127, 61/836,101, 61/836,080, 61/835,973, and 61/835,931, filed Jun. 17, 2013; 62/010,888 and 62/010,879, both filed Jun. 11, 2014; 62/010,329 and 62/010,441, each filed Jun. 10, 2014; 61/939,228 and 61/939,242, each filed Feb. 12, 2014; 61/980,012, filed Apr. 15,2014; 62/038,358, filed Aug. 17, 2014; 62/054,490, 62/055,484, 62/055,460 and 62/055,487, each filed Sep. 25, 2014; and 62/069,243, filed Oct. 27, 2014. Reference is also made to U.S. provisional patent applications Nos. 62/055,484, 62/055,460, and 62/055,487, filed Sep. 25, 2014; U.S. provisional patent application 61/980,012, filed Apr. 15, 2014; and U.S. provisional patent application 61/939,242 filed Feb. 12, 2014. Reference is made to PCT application designating, inter alia, the United States, application No. PCT/US14/41806, filed Jun. 10, 2014. Reference is made to U.S. provisional patent application 61/930,214 filed on Jan. 22, 2014. Reference is made to U.S. provisional patent applications 61/915,251; 61/915,260 and 61/915,267, each filed on Dec. 12, 2013. Reference is made to U.S. provisional patent application Ser. No. 61/980,012 filed Apr. 15, 2014. Reference is made to PCT application designating, inter alia, the United States, application No. PCT/US14/41806, filed Jun. 10, 2014. Reference is made to U.S. provisional patent application 61/930,214 filed on Jan. 22, 2014. Reference is made to U.S. provisional patent applications 61/915,251; 61/915,260 and 61/915,267, each filed on Dec. 12, 2013. 
     Mention is also made of U.S. application 62/091,455, filed, 12 Dec. 14, PROTECTED GUIDE RNAS (PGRNAS); U.S. application 62/096,708, 24 Dec. 14, PROTECTED GUIDE RNAS (PGRNAS); U.S. application 62/091,462, 12 Dec. 14, DEAD GUIDES FOR CRISPR TRANSCRIPTION FACTORS; U.S. application 62/096,324, 23 Dec. 14, DEAD GUIDES FOR CRISPR TRANSCRIPTION FACTORS; U.S. application 62/091,456, 12 Dec. 14, ESCORTED AND FUNCTIONALIZED GUIDES FOR CRISPR-CAS SYSTEMS; U.S. application 62/091,461, 12 Dec. 14, DELIVERY, USE AND THERAPEUTIC APPLICATIONS OF THE CRISPR-CAS SYSTEMS AND COMPOSITIONS FOR GENOME EDITING AS TO HEMATOPOETIC STEM CELLS (HSCs); U.S. application 62/094,903, 19 Dec. 14, UNBIASED IDENTIFICATION OF DOUBLE-STRAND BREAKS AND GENOMIC REARRANGEMENT BY GENOME-WISE INSERT CAPTURE SEQUENCING; U.S. application 62/096,761, 24 Dec. 14, ENGINEERING OF SYSTEMS, METHODS AND OPTIMIZED ENZYME AND GUIDE SCAFFOLDS FOR SEQUENCE MANIPULATION; U.S. application 62/098,059, 30 Dec. 14, RNA-TARGETING SYSTEM; U.S. application 62/096,656, 24 Dec. 14, CRISPR HAVING OR ASSOCIATED WITH DESTABILIZATION DOMAINS; U.S. application 62/096,697, 24 Dec. 14, CRISPR HAVING OR ASSOCIATED WITH AAV; U.S. application 62/098,158, 30 Dec. 14, ENGINEERED CRISPR COMPLEX INSERTIONAL TARGETING SYSTEMS; U.S. application 62/151,052, 22 Apr. 15, CELLULAR TARGETING FOR EXTRACELLULAR EXOSOMAL REPORTING; U.S. application 62/054,490, 24 Sep. 14, DELIVERY, USE AND THERAPEUTIC APPLICATIONS OF THE CRISPR-CAS SYSTEMS AND COMPOSITIONS FOR TARGETING DISORDERS AND DISEASES USING PARTICLE DELIVERY COMPONENTS; U.S. application 62/055,484, 25 Sep. 14, SYSTEMS, METHODS AND COMPOSITIONS FOR SEQUENCE MANIPULATION WITH OPTIMIZED FUNCTIONAL CRISPR-CAS SYSTEMS; U.S. application 62/087,537, 4 Dec. 14, SYSTEMS, METHODS AND COMPOSITIONS FOR SEQUENCE MANIPULATION WITH OPTIMIZED FUNCTIONAL CRISPR-CAS SYSTEMS; U.S. application 62/054,651, 24 Sep. 14, DELIVERY, USE AND THERAPEUTIC APPLICATIONS OF THE CRISPR-CAS SYSTEMS AND COMPOSITIONS FOR MODELING COMPETITION OF MULTIPLE CANCER MUTATIONS IN VIVO; U.S. application 62/067,886, 23 Oct. 14, DELIVERY, USE AND THERAPEUTIC APPLICATIONS OF THE CRISPR-CAS SYSTEMS AND COMPOSITIONS FOR MODELING COMPETITION OF MULTIPLE CANCER MUTATIONS IN VIVO; U.S. application 62/054,675, 24 Sep. 14, DELIVERY, USE AND THERAPEUTIC APPLICATIONS OF THE CRISPR-CAS SYSTEMS AND COMPOSITIONS IN NEURONAL CELLS/TISSUES; U.S. application 62/054,528, 24 Sep. 14, DELIVERY, USE AND THERAPEUTIC APPLICATIONS OF THE CRISPR-CAS SYSTEMS AND COMPOSITIONS IN IMMUNE DISEASES OR DISORDERS; U.S. application 62/055,454, 25 Sep. 14, DELIVERY, USE AND THERAPEUTIC APPLICATIONS OF THE CRISPR-CAS SYSTEMS AND COMPOSITIONS FOR TARGETING DISORDERS AND DISEASES USING CELL PENETRATION PEPTIDES (CPP); U.S. application 62/055,460, 25 Sep. 14, MULTIFUNCTIONAL-CRISPR COMPLEXES AND/OR OPTIMIZED ENZYME LINKED FUNCTIONAL-CRISPR COMPLEXES; U.S. application 62/087,475, 4 Dec. 14, FUNCTIONAL SCREENING WITH OPTIMIZED FUNCTIONAL CRISPR-CAS SYSTEMS; U.S. application 62/055,487, 25 Sep. 14, FUNCTIONAL SCREENING WITH OPTIMIZED FUNCTIONAL CRISPR-CAS SYSTEMS; U.S. application 62/087,546, 4 Dec. 14, MULTIFUNCTIONAL CRISPR COMPLEXES AND/OR OPTIMIZED ENZYME LINKED FUNCTIONAL-CRISPR COMPLEXES; and U.S. application 62/098,285, 30 Dec. 14, CRISPR MEDIATED IN VIVO MODELING AND GENETIC SCREENING OF TUMOR GROWTH AND METASTASIS. 
     Each of these patents, patent publications, and applications, and all documents cited therein or during their prosecution (“appin cited documents”) and all documents cited or referenced in the appin cited documents, together with any instructions, descriptions, product specifications, and product sheets for any products mentioned therein or in any document therein and incorporated by reference herein, are hereby incorporated herein by reference, and may be employed in the practice of the invention. All documents (e.g., these patents, patent publications and applications and the appin cited documents) are incorporated herein by reference to the same extent as if each individual document was specifically and individually indicated to be incorporated by reference. 
     Also with respect to general information on CRISPR-Cas Systems, mention is made of the following (also hereby incorporated herein by reference):
         Multiplex genome engineering using CRISPR/Cas systems. Cong, L., Ran, F. A., Cox, D., Lin, S., Barretto, R., Habib, N., Hsu, P. D., Wu, X., Jiang, W., Marraffini, L. A., &amp; Zhang, F. Science February 15; 339(6121):819-23 (2013);   RNA-guided editing of bacterial genomes using CRISPR-Cas systems. Jiang W., Bikard D., Cox D., Zhang F, Marraffini LA. Nat Biotechnol March; 31(3):233-9 (2013);   One-Step Generation of Mice Carrying Mutations in Multiple Genes by CRISPR/Cas-Mediated Genome Engineering. Wang H., Yang H., Shivalila C S., Dawlaty M M., Cheng A W., Zhang F., Jaenisch R. Cell May 9; 153(4):910-8 (2013);   Optical control of mammalian endogenous transcription and epigenetic states. Konermann S, Brigham M D, Trevino A E, Hsu P D, Heidenreich M, Cong L, Platt R J, Scott D A, Church G M, Zhang F. Nature. August 22; 500(7463):472-6. doi: 10.1038/Nature12466. Epub 2013 Aug. 23 (2013);   Double Nicking by RNA-Guided CRISPR Cas9 for Enhanced Genome Editing Specificity. Ran, F A., Hsu, P D., Lin, C Y., Gootenberg, J S., Konermann, S., Trevino, A E., Scott, D A., Inoue, A., Matoba, S., Zhang, Y., &amp; Zhang, F. Cell August 28. pii: S0092-8674(13)01015-5 (2013-A);   DNA targeting specificity of RNA-guided Cas9 nucleases. Hsu, P., Scott, D., Weinstein, J., Ran, F A., Konermann, S., Agarwala, V., Li, Y., Fine, E., Wu, X., Shalem, O., Cradick, T J., Marraffini, L A., Bao, G., &amp; Zhang, F. Nat Biotechnol doi:10.1038/nbt.2647 (2013);   Genome engineering using the CRISPR-Cas9 system. Ran, F A., Hsu, P D., Wright, J., Agarwala, V., Scott, D A., Zhang, F. Nature Protocols November; 8(11):2281-308 (2013-B);   Genome-Scale CRISPR-Cas9 Knockout Screening in Human Cells. Shalem, O., Sanjana, N E., Hartenian, E., Shi, X., Scott, D A., Mikkelson, T., Heckl, D., Ebert, B L., Root, D E., Doench, J G., Zhang, F. Science December 12. (2013). [Epub ahead of print];   Crystal structure of cas9 in complex with guide RNA and target DNA. Nishimasu, H., Ran, F A., Hsu, P D., Konermann, S., Shehata, S I., Dohmae, N., Ishitani, R., Zhang, F., Nureki, O. Cell Feburary 27, 156(5):935-49 (2014);   Genome-wide binding of the CRISPR endonuclease Cas9 in mammalian cells. Wu X., Scott D A., Kriz A J., Chiu A C., Hsu P D., Dadon D B., Cheng A W., Trevino A E., Konermann S., Chen S., Jaenisch R., Zhang F., Sharp P A. Nat Biotechnol. April 20. doi: 10.1038/nbt.2889 (2014);   CRISPR-Cas9 Knockin Mice for Genome Editing and Cancer Modeling. Platt R J, Chen S, Zhou Y, Yim M J, Swiech L, Kempton H R, Dahlman J E, Parnas O, Eisenhaure T M, Jovanovic M, Graham D B, Jhunjhunwala S, Heidenreich M, Xavier R J, Langer R, Anderson D G, Hacohen N, Regev A, Feng G, Sharp PA, Zhang F. Cell 159(2): 440-455 DOI: 10.1016/j.ce11.2014.09.014(2014);   Development and Applications of CRISPR-Cas9 for Genome Engineering, Hsu P D, Lander E S, Zhang F., Cell. June 5; 157(6):1262-78 (2014).   Genetic screens in human cells using the CRISPR/Cas9 system, Wang T, Wei J J, Sabatini D M, Lander E S., Science. January 3; 343(6166): 80-84. doi:10.1126/science.1246981 (2014);   Rational design of highly active sgRNAs for CRISPR-Cas9-mediated gene inactivation, Doench J G, Hartenian E, Graham D B, Tothova Z, Hegde M, Smith I, Sullender M, Ebert B L, Xavier R J, Root D E., (published online 3 Sep. 2014) Nat Biotechnol. December; 32(12):1262-7 (2014);   In vivo interrogation of gene function in the mammalian brain using CRISPR-Cas9, Swiech L, Heidenreich M, Banerjee A, Habib N, Li Y, Trombetta J, Sur M, Zhang F., (published online 19 Oct. 2014) Nat Biotechnol. January; 33(1):102-6 (2015);   Genome-scale transcriptional activation by an engineered CRISPR-Cas9 complex, Konermann S, Brigham M D, Trevino A E, Joung J, Abudayyeh O O, Barcena C, Hsu PD, Habib N, Gootenberg J S, Nishimasu H, Nureki O, Zhang F., Nature. Janurary 29; 517(7536):583-8 (2015).   A split-Cas9 architecture for inducible genome editing and transcription modulation, Zetsche B, Volz S E, Zhang F., (published online 2 Feb. 2015) Nat Biotechnol. February; 33(2):139-42 (2015);   Genome-wide CRISPR Screen in a Mouse Model of Tumor Growth and Metastasis, Chen S, Sanjana N E, Zheng K, Shalem O, Lee K, Shi X, Scott D A, Song J, Pan J Q, Weissleder R, Lee H, Zhang F, Sharp P A. Cell 160, 1246-1260, Mar. 12, 2015 (multiplex screen in mouse), and   In vivo genome editing using  Staphylococcus aureus  Cas9, Ran F A, Cong L, Yan W X, Scott D A, Gootenberg J S, Kriz A J, Zetsche B, Shalem O, Wu X, Makarova K S, Koonin E V, Sharp P A, Zhang F., (published online 1 Apr. 2015), Nature. April 9; 520(7546):186-91 (2015).   Shalem et al., “High-throughput functional genomics using CRISPR-Cas9,” Nature Reviews Genetics 16, 299-311 (May 2015).   Xu et al., “Sequence determinants of improved CRISPR sgRNA design,” Genome Research 25, 1147-1157 (August 2015).   Parnas et al., “A Genome-wide CRISPR Screen in Primary Immune Cells to Dissect Regulatory Networks,” Cell 162, 675-686 (Jul. 30, 2015).   Ramanan et al., CRISPR/Cas9 cleavage of viral DNA efficiently suppresses hepatitis B virus,” Scientific Reports 5:10833. doi: 10.1038/srep10833 (Jun. 2, 2015)   Nishimasu et al., Crystal Structure of Staphylococcus aureus Cas9,” Cell 162, 1113-1126 (Aug. 27, 2015)   Zetsche et al., “Cpf1 Is a Single RNA-Guided Endonuclease of a Class 2 CRISPR-Cas System, ” Cell 163, 1-13 (Oct. 22, 2015)   Shmakov et al., “Discovery and Functional Characterization of Diverse Class 2 CRISPR-Cas Systems,” Molecular Cell 60, 1-13 (Available online Oct. 22, 2015) each of which is incorporated herein by reference, may be considered in the practice of the instant invention, and discussed briefly below:   Cong et al. engineered type II CRISPR-Cas systems for use in eukaryotic cells based on both Streptococcus thermophilus Cas9 and also Streptococcus pyogenes Cas9 and demonstrated that Cas9 nucleases can be directed by short RNAs to induce precise cleavage of DNA in human and mouse cells. Their study further showed that Cas9 as converted into a nicking enzyme can be used to facilitate homology-directed repair in eukaryotic cells with minimal mutagenic activity. Additionally, their study demonstrated that multiple guide sequences can be encoded into a single CRISPR array to enable simultaneous editing of several at endogenous genomic loci sites within the mammalian genome, demonstrating easy programmability and wide applicability of the RNA-guided nuclease technology. This ability to use RNA to program sequence specific DNA cleavage in cells defined a new class of genome engineering tools. These studies further showed that other CRISPR loci are likely to be transplantable into mammalian cells and can also mediate mammalian genome cleavage. Importantly, it can be envisaged that several aspects of the CRISPR-Cas system can be further improved to increase its efficiency and versatility.   Jiang et al. used the clustered, regularly interspaced, short palindromic repeats (CRISPR)-associated Cas9 endonuclease complexed with dual-RNAs to introduce precise mutations in the genomes of  Streptococcus pneumoniae  and  Escherichia coli.  The approach relied on dual-RNA:Cas9-directed cleavage at the targeted genomic site to kill unmutated cells and circumvents the need for selectable markers or counter-selection systems. The study reported reprogramming dual-RNA:Cas9 specificity by changing the sequence of short CRISPR RNA (crRNA) to make single- and multinucleotide changes carried on editing templates. The study showed that simultaneous use of two crRNAs enabled multiplex mutagenesis. Furthermore, when the approach was used in combination with recombineering, in  S. pneumoniae,  nearly 100% of cells that were recovered using the described approach contained the desired mutation, and in  E. coli,  65% that were recovered contained the mutation.   Wang et al. (2013) used the CRISPR/Cas system for the one-step generation of mice carrying mutations in multiple genes which were traditionally generated in multiple steps by sequential recombination in embryonic stem cells and/or time-consuming intercrossing of mice with a single mutation. The CRISPR/Cas system will greatly accelerate the in vivo study of functionally redundant genes and of epistatic gene interactions.   Konermann et al. (2013) addressed the need in the art for versatile and robust technologies that enable optical and chemical modulation of DNA-binding domains based CRISPR Cas9 enzyme and also Transcriptional Activator Like Effectors   Ran et al. (2013-A) described an approach that combined a Cas9 nickase mutant with paired guide RNAs to introduce targeted double-strand breaks. This addresses the issue of the Cas9 nuclease from the microbial CRISPR-Cas system being targeted to specific genomic loci by a guide sequence, which can tolerate certain mismatches to the DNA target and thereby promote undesired off-target mutagenesis. Because individual nicks in the genome are repaired with high fidelity, simultaneous nicking via appropriately offset guide RNAs is required for double-stranded breaks and extends the number of specifically recognized bases for target cleavage. The authors demonstrated that using paired nicking can reduce off-target activity by 50- to 1,500-fold in cell lines and to facilitate gene knockout in mouse zygotes without sacrificing on-target cleavage efficiency. This versatile strategy enables a wide variety of genome editing applications that require high specificity.   Hsu et al. (2013) characterized SpCas9 targeting specificity in human cells to inform the selection of target sites and avoid off-target effects. The study evaluated &gt;700 guide RNA variants and SpCas9-induced indel mutation levels at &gt;100 predicted genomic off-target loci in 293T and 293FT cells. The authors that SpCas9 tolerates mismatches between guide RNA and target DNA at different positions in a sequence-dependent manner, sensitive to the number, position and distribution of mismatches. The authors further showed that SpCas9-mediated cleavage is unaffected by DNA methylation and that the dosage of SpCas9 and sgRNA can be titrated to minimize off-target modification. Additionally, to facilitate mammalian genome engineering applications, the authors reported providing a web-based software tool to guide the selection and validation of target sequences as well as off-target analyses.   Ran et al. (2013-B) described a set of tools for Cas9-mediated genome editing via non-homologous end joining (NHEJ) or homology-directed repair (HDR) in mammalian cells, as well as generation of modified cell lines for downstream functional studies. To minimize off-target cleavage, the authors further described a double-nicking strategy using the Cas9 nickase mutant with paired guide RNAs. The protocol provided by the authors experimentally derived guidelines for the selection of target sites, evaluation of cleavage efficiency and analysis of off-target activity. The studies showed that beginning with target design, gene modifications can be achieved within as little as 1-2 weeks, and modified clonal cell lines can be derived within 2-3 weeks.   Shalem et al. described a new way to interrogate gene function on a genome-wide scale. Their studies showed that delivery of a genome-scale CRISPR-Cas9 knockout (GeCKO) library targeted 18,080 genes with 64,751 unique guide sequences enabled both negative and positive selection screening in human cells. First, the authors showed use of the GeCKO library to identify genes essential for cell viability in cancer and pluripotent stem cells. Next, in a melanoma model, the authors screened for genes whose loss is involved in resistance to vemurafenib, a therapeutic that inhibits mutant protein kinase BRAF. Their studies showed that the highest-ranking candidates included previously validated genes NF1 and MED12 as well as novel hits NF2, CUL3, TADA2B, and TADA1. The authors observed a high level of consistency between independent guide RNAs targeting the same gene and a high rate of hit confirmation, and thus demonstrated the promise of genome-scale screening with Cas9.   Nishimasu et al. reported the crystal structure of Streptococcus pyogenes Cas9 in complex with sgRNA and its target DNA at 2.5 A° resolution. The structure revealed a bilobed architecture composed of target recognition and nuclease lobes, accommodating the sgRNA:DNA heteroduplex in a positively charged groove at their interface. Whereas the recognition lobe is essential for binding sgRNA and DNA, the nuclease lobe contains the HNH and RuvC nuclease domains, which are properly positioned for cleavage of the complementary and non-complementary strands of the target DNA, respectively. The nuclease lobe also contains a carboxyl-terminal domain responsible for the interaction with the protospacer adjacent motif (PAM). This high-resolution structure and accompanying functional analyses have revealed the molecular mechanism of RNA-guided DNA targeting by Cas9, thus paving the way for the rational design of new, versatile genome-editing technologies.   Wu et al. mapped genome-wide binding sites of a catalytically inactive Cas9 (dCas9) from Streptococcus pyogenes loaded with single guide RNAs (sgRNAs) in mouse embryonic stem cells (mESCs). The authors showed that each of the four sgRNAs tested targets dCas9 to between tens and thousands of genomic sites, frequently characterized by a 5-nucleotide seed region in the sgRNA and an NGG protospacer adjacent motif (PAM). Chromatin inaccessibility decreases dCas9 binding to other sites with matching seed sequences; thus 70% of off-target sites are associated with genes. The authors showed that targeted sequencing of 295 dCas9 binding sites in mESCs transfected with catalytically active Cas9 identified only one site mutated above background levels. The authors proposed a two-state model for Cas9 binding and cleavage, in which a seed match triggers binding but extensive pairing with target DNA is required for cleavage.   Platt et al. established a Cre-dependent Cas9 knockin mouse. The authors demonstrated in vivo as well as ex vivo genome editing using adeno-associated virus (AAV)-, lentivirus-, or particle-mediated delivery of guide RNA in neurons, immune cells, and endothelial cells.   Hsu et al. (2014) is a review article that discusses generally CRISPR-Cas9 history from yogurt to genome editing, including genetic screening of cells.   Wang et al. (2014) relates to a pooled, loss-of-function genetic screening approach suitable for both positive and negative selection that uses a genome-scale lentiviral single guide RNA (sgRNA) library.   Doench et al. created a pool of sgRNAs, tiling across all possible target sites of a panel of six endogenous mouse and three endogenous human genes and quantitatively assessed their ability to produce null alleles of their target gene by antibody staining and flow cytometry. The authors showed that optimization of the PAM improved activity and also provided an on-line tool for designing sgRNAs.   Swiech et al. demonstrate that AAV-mediated SpCas9 genome editing can enable reverse genetic studies of gene function in the brain.   Konermann et al. (2015) discusses the ability to attach multiple effector domains, e.g., transcriptional activator, functional and epigenomic regulators at appropriate positions on the guide such as stem or tetraloop with and without linkers.   Zetsche et al. demonstrates that the Cas9 enzyme can be split into two and hence the assembly of Cas9 for activation can be controlled.   Chen et al. relates to multiplex screening by demonstrating that a genome-wide in vivo CRISPR-Cas9 screen in mice reveals genes regulating lung metastasis.   Ran et al. (2015) relates to SaCas9 and its ability to edit genomes and demonstrates that one cannot extrapolate from biochemical assays.   Shalem et al. (2015) described ways in which catalytically inactive Cas9 (dCas9) fusions are used to synthetically repress (CRISPRi) or activate (CRISPRa) expression, showing. advances using Cas9 for genome-scale screens, including arrayed and pooled screens, knockout approaches that inactivate genomic loci and strategies that modulate transcriptional activity.   Xu et al. (2015) assessed the DNA sequence features that contribute to single guide RNA (sgRNA) efficiency in CRISPR-based screens. The authors explored efficiency of CRISPR/Cas9 knockout and nucleotide preference at the cleavage site. The authors also found that the sequence preference for CRISPRi/a is substantially different from that for CRISPR/Cas9 knockout.   Parnas et al. (2015) introduced genome-wide pooled CRISPR-Cas9 libraries into dendritic cells (DCs) to identify genes that control the induction of tumor necrosis factor (Tnf) by bacterial lipopolysaccharide (LPS). Known regulators of T1r4 signaling and previously unknown candidates were identified and classified into three functional modules with distinct effects on the canonical responses to LPS.   Ramanan et al (2015) demonstrated cleavage of viral episomal DNA (cccDNA) in infected cells. The HBV genome exists in the nuclei of infected hepatocytes as a 3.2 kb double-stranded episomal DNA species called covalently closed circular DNA (cccDNA), which is a key component in the HBV life cycle whose replication is not inhibited by current therapies. The authors showed that sgRNAs specifically targeting highly conserved regions of HBV robustly suppresses viral replication and depleted cccDNA.   Nishimasu et al. (2015) reported the crystal structures of SaCas9 in complex with a single guide RNA (sgRNA) and its double-stranded DNA targets, containing the 5′-TTGAAT-3′ PAM and the 5′-TTGGGT-3′ PAM. A structural comparison of SaCas9 with SpCas9 highlighted both structural conservation and divergence, explaining their distinct PAM specificities and orthologous sgRNA recognition.   Zetsche et al. (2015) reported the characterization of Cpf1, a putative class 2 CRISPR effector. It was demonstrated that Cpf1 mediates robust DNA interference with features distinct from Cas9. Identifying this mechanism of interference broadens our understanding of CRISPR-Cas systems and advances their genome editing applications.   Shmakov et al. (2015) reported the characterization of 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.       

     Methods for Identifying Class 2 Crispr-Cas Effectors 
     Many embodiments disclosed herein relates to a method of identifying novel CRISPR effectors, comprising: a) identifying sequences in a genomic or metagenomic database encoding a CRISPR array; b) identifying one or more Open Reading Frames (ORFs) in said selected sequences within 10 kb of the CRISPR array; c) discarding all loci encoding proteins which are assigned to known CRISPR-Cas subtypes and, optionally, all loci encoding a protein of less than 700 amino acids; and d) identifying putative novel CRISPR effectors, and optionally classifying them based on structure analysis. 
     In some embodiments, the CRISPR effector is a Class 2 CRISPR effector. 
     In some embodiments, step (a) comprises (i) comparing sequences in a genomic and/or metagenomic database with at least one pre-identified seed sequence that encodes a CRISPR array, and selecting sequences comprising said seed sequence; or (ii) identifying CRISPR arrays based on a CRISPR algorithm. 
     In some embodiments, step (d) comprises identifying nuclease domains. 
     In some embodiments, step (d) comprises identifying RuvC, HPN, and/or HEPN domains. 
     In some embodiments, within 10 kb of the CRISPR array no ORF encoding Cas1 or Cas2 is present. 
     In some embodiments, said ORF in step (b) encode a protein of at least 300 amino acids, preferably between 300 and 700 amino acids. 
     In some embodiments, putative novel CRISPR effectors obtained in step (d) are used as seed sequences for further comparing genomic and/or metagenomics sequences and subsequent selecting loci of interest as described in steps a) to d). 
     In some embodiments, the pre-identified seed sequence is obtained by a method comprising: (a) identifying CRISPR motifs in a genomic or metagenomic database, (b) extracting multiple features in said identified CRISPR motifs, (c) classifying the CRISPR loci using unsupervised learning, (d) identifying conserved locus elements based on said classification, and (e) selecting therefrom a putative CRISPR effector suitable as seed sequence. 
     In some embodiments, said features include protein elements, repeat structure, repeat sequence, spacer sequence and spacer mapping. 
     In some embodiments, said genomic and metagenomic databases are bacterial and/or archaeal genomes. 
     In some embodiments, said genomic and metagenomic sequences are obtained from the Ensembl and/or NCBI genome databases. 
     In some embodiments, the structure analysis in step (d) is based on secondary structure prediction and/or sequence alignments. 
     In some embodiments, step d) is achieved by clustering of the remaining loci based on the proteins they encode and manual curation of the obtained clusters. 
     In some embodiments, the clustering of the remaining loci and manual curation of the obtained clusters is performed by sensitive profile-based methods such as HHpred, secondary structure prediction and manual examination of multiple alignments and discarding the loci encoding protein domains deemed irrelevant in the context of the CRISPR-Cas function. 
     In some embodiments, loci encoding proteins (i) which match with low HHpred homology to any known protein domain, (ii) with minimal existing CRISPR classifications, (iii) which are located at 2 kb or less than 2 kb from the seed sequence, (iv) which have an identical orientation with respect to putative adjacent accessory proteins, (v) with consistent nature of CRISPR arrays nearby similar proteins, and (vi) with few neighboring annotated CRISPR proteins, are selected as candidate Class 2 CRISPR loci. 
     Moreover, many embodiments disclosed herein relates a method for identifying putative CRISPR effectors comprising (a) identifying multiple CRISPR motifs using genome sequencing data; (b) extracting multiple features from said identified CRISPR motifs, such as protein elements, repeat structure, repeat sequence, spacer sequence and spacer mapping; (c) classifying CRISPR loci based on these features using unsupervised learning; (d) identifying conserved locus elements; and (e) selecting therefrom putative CRISPR effector based on structure analysis. 
     Furthermore, many embodiments disclosed herein relates a method of identifying a Class 2 CRISPR effector, comprising: a) comparing sequences in a genomic and/or metagenomic database with at least one pre-identified seed sequence that encodes a CRISPR array, and selecting sequences comprising said seed sequence; b) identifying one or more Open Reading Frames (ORFs) in said selected sequences within 10 kb of the CRISPR array, wherein the ORF encode a protein of at least 300 amino acids and comprising one or more RuvC, HPN, and/or HEPN domains; and c) identifying putative novel CRISPR effectors, and optionally classifying them based on structure analysis. 
     Novel Class 2 Crispr-Cas Effectors 
     Many embodiments disclosed herein relates to novel Class 2 CRISPR effectors that have been newly identified. 
     In some embodiment, a recombinant nucleic acid is provided, which comprising a nucleic acid sequence encoding a Class 2 CRISPR effector operably linked to a heterologous promoter, wherein the Class 2 CRISPR effector is not Cas9, Cpf1, C2c1, C2c2, C2c3, and C2c6. 
     In some embodiments, the Class 2 CRISPR effector is a Type V CRISPR effector. 
     In some embodiments, the Class 2 CRISPR effector has about 300 and 700 amino acids. 
     In some embodiments, the Class 2 CRISPR effector comprises a RuvC-like nuclease domain. 
     In some embodiments, the Class 2 CRISPR effector is a nuclease adapted to break an DNA strand. 
     In some embodiments, the Class 2 CRISPR effector is an endogenous protein of  Clostridium botulinum  strain 713 CBOT 382, Peptoclostridium difficile P20, Peptoclostridium difficile DA00114,  Clostridium hiranonis  DSM 13275, Cellulosilyticum ruminicola JCM 14822,  Clostridium novyi  B str NCTC 9691,  Clostridium botulinum  strain AM1195 AM1195 7,  Clostridium ljungdahlii  DSM 13528,  Bacillus mycoides  Rock3 17,  Bacillus cereus  MC67,  Ruminococcus albus  7,  Ruminococcus albus  SY3,  Eubacterium siraeum  DSM 15702,  Clostridium anorexicamassiliense  AP5,  Clostridium novyi  B str NCTC 9691,  Clostridium pasteurianum  BC1,  Thermincola ferriacetica, Syntrophomonas palmitatica  JCM 14374,  Bacillus cereus, Bacillus cereus  H308197,  Bacillus cereus  strain Lr 2 Apr LG48 098,  Bacillus thuringiensis  HD 771,  Sulfurihydrogenibium azorense  Az Fu1, or  Hydrogenivirga  sp 128 5 R1 1. 
     In some embodiments, the Class 2 CRISPR effector is an endogenous protein of Microcoleus PCC 7113, Lyngbya aestuarii BL J, Lyngbya sp PCC 8106, Cyanothece PCC 8801, Cyanothece sp PCC 8802, Chamaesiphon minutus PCC 6605, Microcystis aeruginosa PCC 9432, or Dolichospermum circinale AWQC310F. 
     In some embodiments, the Class 2 CRISPR effector is an endogenous protein of Mycobacterium conceptionense, Gordonia otitidis NBRC 100426, Mycobacterium mucogenicum strain CCH10 A2, Gordonia polyisoprenivorans VH2, Arthrospira platensis NIES 39, Halothece PCC 7418, Halothece PCC 7418, Stanieria cyanosphaera PCC 7437, Oscillatoria PCC 7112, Halorhodospira halophila SL1, Meiothermus silvanus DSM 9946, Pelobacter propionicus DSM 2379, Clostridiales bacterium DRI 13 BR63. 
     In some embodiments, the Class 2 CRISPR effector is an endogenous protein of Propionimicrobium lymphophilum ACS 093, Blastococcus saxobsidens DD2, Micrococcus luteus strain 773, Corynebacterium maris DSM 45190, Corynebacterium glutamicum, Rothia dentocariosa M567, Rothia mucilaginosa strain 1211,  Streptococcus parasanguinis  strain 348,  Rothia mucilaginosa  strain 473, Cellulosimicrobium cellulans LMG 16121, Dermacoccus sp Ellin185,  Streptomyces  sp NRRL S 378,  Streptomyces regensis, Streptomyces  sp,  Streptomyces  sp SPB74,  Streptomyces wadayamensis, Streptomyces rimosus  subsp rimosus, Kitasatospora cheerisanensis KCTC 2395, Nocardiopsis synnemataformans DSM 44143, Nocardiopsis alba DSM 43377,  Streptomyces niveus NCIMB  11891,  Mycobacterium smegmatis  J5623,  Mycobacterium yongonense  05 1390,  Mycobacterium  sp UM RHS Contig 9,  Streptomyces  sp CNH099 B121, or Nocardioides JS614. 
     In some embodiments, the Class 2 CRISPR effector is an endogenous protein of Nodosilinea nodulosa PCC 7104, Lyngbya confervoides BDU141951, Leptolyngbya boryana PCC 6306, Geminocystis NIES 3709, Geminocystis NIES 3708, Myxosarcina GI1 GI1, Xenococcus PCC 7305, Cyanothece CCY0110, Cyanothece PCC 8801, Gloeocapsa PCC 73106, Cyanothece PCC 8802, Halothece PCC 7418, Crinalium epipsammum PCC 9333, Microcoleus PCC 7113, Nostoc punctiforme PCC 73102, Scytonema hofmanni UTEX 2349, Hassallia byssoidea VB512170, Nostoc PCC 7120, Scytonema millei VB511283, Anabaena variabilis ATCC 29413, Tolypothrix PCC 7601 UTEX B 481, Anabaena WA102, Anabaena cylindrica PCC 7122, Mastigocoleus testarum BC008, Cyanothece PCC 8801, Scytonema hofmanni PCC 7110, Calothrix PCC 7103 PCC 7103, Calothrix PCC 6303, Cyanothece PCC 8801, Crinalium epipsammum PCC 9333, Microcoleus PCC 7113, Geitlerinema PCC 7407, Cyanothece PCC 7425, Chamaesiphon minutus PCC 6605, or Tolypothrix PCC 7601 UTEX B 481. 
     In some embodiments, the Class 2 CRISPR effector is a Type VI CRISPR effector. 
     In some embodiments, the Class 2 CRISPR effector comprises at least one HEPN nuclease domain. 
     In some embodiments, the Class 2 CRISPR effector comprises at least two HEPN nuclease domains. 
     In some embodiments, the Class 2 CRISPR effector is a nuclease adapted to break an RNA strand. 
     In some embodiments, the Class 2 CRISPR effector is an endogenous protein of Fusobacterium perfoetens. 
     In some embodiments, an expression cassette is provided, which comprises the recombinant nucleic acid. 
     In some embodiments, a vector is provided, which comprises the expression cassette. 
     In some embodiments, a cell is provided which has been transformed with the vector. 
     Additional Embodiments 
     In general, the CRISPR-Cas or CRISPR system is as used in the foregoing documents, such as WO 2014/093622 (PCT/US2013/074667) and refers collectively to transcripts and other elements involved in the expression of or directing the activity of CRISPR-associated (“Cas”) genes, including sequences encoding a Cas gene, a tracr (trans-activating CRISPR) sequence (e.g. tracrRNA or an active partial tracrRNA), a tracr-mate sequence (encompassing a “direct repeat” and a tracrRNA-processed partial direct repeat in the context of an endogenous CRISPR system), a guide sequence (also referred to as a “spacer” in the context of an endogenous CRISPR system), or “RNA(s)” as that term is herein used (e.g., RNA(s) to guide Cas, such as Cas9, e.g. CRISPR RNA and transactivating (tracr) RNA or a single guide RNA (sgRNA) (chimeric RNA)) or other sequences and transcripts from a CRISPR locus. In general, a CRISPR system is characterized by elements that promote the formation of a CRISPR complex at the site of a target sequence (also referred to as a protospacer in the context of an endogenous CRISPR system). In the context of formation of a CRISPR complex, “target sequence” refers to a sequence to which a guide sequence is designed to have complementarity, where hybridization between a target sequence and a guide sequence promotes the formation of a CRISPR complex. A target sequence may comprise any polynucleotide, such as DNA or RNA polynucleotides. In some embodiments, a target sequence is located in the nucleus or cytoplasm of a cell. In some embodiments, direct repeats may be identified in silico by searching for repetitive motifs that fulfill any or all of the following criteria: 1. found in a 2Kb window of genomic sequence flanking the type II CRISPR locus; 2. span from 20 to 50 bp; and 3. interspaced by 20 to 50 bp. In some embodiments, 2 of these criteria may be used, for instance 1 and 2, 2 and 3, or 1 and 3. In some embodiments, all 3 criteria may be used. 
     In embodiments of the invention the terms guide sequence and guide RNA, i.e. RNA capable of guiding Cas to a target genomic locus, are used interchangeably as in foregoing cited documents such as WO 2014/093622 (PCT/US2013/074667). In general, a guide sequence is any polynucleotide sequence having sufficient complementarity with a target polynucleotide sequence to hybridize with the target sequence and direct sequence-specific binding of a CRISPR complex to the target sequence. In some embodiments, the degree of complementarity between a guide sequence and its corresponding target sequence, when optimally aligned using a suitable alignment algorithm, is about or more than about 50%, 60%, 75%, 80%, 85%, 90%, 95%, 97.5%, 99%, or more. Optimal alignment may be determined with the use of any suitable algorithm for aligning sequences, non-limiting example of which include the Smith-Waterman algorithm, the Needleman-Wunsch algorithm, algorithms based on the Burrows-Wheeler Transform (e.g. the Burrows Wheeler Aligner), ClustalW, Clustal X, BLAT, Novoalign (Novocraft Technologies; available at www.novocraft.com), ELAND (Illumina, San Diego, Calif.), SOAP (available at soap.genomics.org.cn), and Maq (available at maq.sourceforge.net). In some embodiments, a guide sequence is about or more than about 5, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 35, 40, 45, 50, 75, or more nucleotides in length. In some embodiments, a guide sequence is less than about 75, 50, 45, 40, 35, 30, 25, 20, 15, 12, or fewer nucleotides in length. Preferably the guide sequence is 10 30 nucleotides long. The ability of a guide sequence to direct sequence-specific binding of a CRISPR complex to a target sequence may be assessed by any suitable assay. For example, the components of a CRISPR system sufficient to form a CRISPR complex, including the guide sequence to be tested, may be provided to a host cell having the corresponding target sequence, such as by transfection with vectors encoding the components of the CRISPR sequence, followed by an assessment of preferential cleavage within the target sequence, such as by Surveyor assay as described herein. Similarly, cleavage of a target polynucleotide sequence may be evaluated in a test tube by providing the target sequence, components of a CRISPR complex, including the guide sequence to be tested and a control guide sequence different from the test guide sequence, and comparing binding or rate of cleavage at the target sequence between the test and control guide sequence reactions. Other assays are possible, and will occur to those skilled in the art. 
     In a classic CRISPR-Cas systems, the degree of complementarity between a guide sequence and its corresponding target sequence can be about or more than about 50%, 60%, 75%, 80%, 85%, 90%, 95%, 97.5%, 99%, or 100%; a guide or RNA or sgRNA can be about or more than about 5, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 35, 40, 45, 50, 75, or more nucleotides in length; or guide or RNA or sgRNA can be less than about 75, 50, 45, 40, 35, 30, 25, 20, 15, 12, or fewer nucleotides in length; and advantageously tracr RNA is 30 or 50 nucleotides in length. However, an aspect of the invention is to reduce off-target interactions, e.g., reduce the guide interacting with a target sequence having low complementarity. Indeed, in the examples, it is shown that the invention involves mutations that result in the CRISPR-Cas system being able to distinguish between target and off-target sequences that have greater than 80% to about 95% complementarity, e.g., 83%-84% or 88-89% or 94-95% complementarity (for instance, distinguishing between a target having 18 nucleotides from an off-target of 18 nucleotides having 1, 2 or 3 mismatches). Accordingly, in the context of the present invention the degree of complementarity between a guide sequence and its corresponding target sequence is greater than 94.5% or 95% or 95.5% or 96% or 96.5% or 97% or 97.5% or 98% or 98.5% or 99% or 99.5% or 99.9%, or 100%. Off target is less than 100% or 99.9% or 99.5% or 99% or 99% or 98.5% or 98% or 97.5% or 97% or 96.5% or 96% or 95.5% or 95% or 94.5% or 94% or 93% or 92% or 91% or 90% or 89% or 88% or 87% or 86% or 85% or 84% or 83% or 82% or 81% or 80% complementarity between the sequence and the guide, with it advantageous that off target is 100% or 99.9% or 99.5% or 99% or 99% or 98.5% or 98% or 97.5% or 97% or 96.5% or 96% or 95.5% or 95% or 94.5% complementarity between the sequence and the guide. 
     In particularly preferred embodiments according to the invention, the guide RNA (capable of guiding Cas to a target locus) may comprise (1) a guide sequence capable of hybridizing to a genomic target locus in the eukaryotic cell; (2) a tracr sequence; and (3) a tracr mate sequence. All (1) to (3) may reside in a single RNA, i.e. an sgRNA (arranged in a 5′ to 3′ orientation), or the tracr RNA may be a different RNA than the RNA containing the guide and tracr sequence. The tracr hybridizes to the tracr mate sequence and directs the CRISPR/Cas complex to the target sequence. 
     The methods according to the invention as described herein comprehend inducing one or more mutations in a eukaryotic cell (in vitro, i.e. in an isolated eukaryotic cell) as herein discussed comprising delivering to cell a vector as herein discussed. The mutation(s) can include the introduction, deletion, or substitution of one or more nucleotides at each target sequence of cell(s) via the guide(s) RNA(s) or sgRNA(s). The mutations can include the introduction, deletion, or substitution of 1-75 nucleotides at each target sequence of said cell(s) via the guide(s) RNA(s) or sgRNA(s). The mutations can include the introduction, deletion, or substitution of 1, 5, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 35, 40, 45, 50, or 75 nucleotides at each target sequence of said cell(s) via the guide(s) RNA(s) or sgRNA(s). The mutations can include the introduction, deletion, or substitution of 5, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 35, 40, 45, 50, or 75 nucleotides at each target sequence of said cell(s) via the guide(s) RNA(s) or sgRNA(s). The mutations include the introduction, deletion, or substitution of 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 35, 40, 45, 50, or 75 nucleotides at each target sequence of said cell(s) via the guide(s) RNA(s) or sgRNA(s). The mutations can include the introduction, deletion, or substitution of 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 35, 40, 45, 50, or 75 nucleotides at each target sequence of said cell(s) via the guide(s) RNA(s) or sgRNA(s). The mutations can include the introduction, deletion, or substitution of 40, 45, 50, 75, 100, 200, 300, 400 or 500 nucleotides at each target sequence of said cell(s) via the guide(s) RNA(s) or sgRNA(s). 
     For minimization of toxicity and off-target effect, it will be important to control the concentration of Cas mRNA and guide RNA delivered. Optimal concentrations of Cas mRNA and guide RNA can be determined by testing different concentrations in a cellular or non-human eukaryote animal model and using deep sequencing the analyze the extent of modification at potential off-target genomic loci. Alternatively, to minimize the level of toxicity and off-target effect, Cas nickase mRNA (for example  S. pyogenes  Cas9 with the D10A mutation) can be delivered with a pair of guide RNAs targeting a site of interest. Guide sequences and strategies to minimize toxicity and off-target effects can be as in WO 2014/093622 (PCT/US2013/074667); or, via mutation as herein. 
     Typically, in the context of an endogenous CRISPR system, formation of a CRISPR complex (comprising a guide sequence hybridized to a target sequence and complexed with one or more Cas proteins) results in cleavage of one or both strands in or near (e.g. within 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 50, or more base pairs from) the target sequence. Without wishing to be bound by theory, the tracr sequence, which may comprise or consist of all or a portion of a wild-type tracr sequence (e.g. about or more than about 20, 26, 32, 45, 48, 54, 63, 67, 85, or more nucleotides of a wild-type tracr sequence), may also form part of a CRISPR complex, such as by hybridization along at least a portion of the tracr sequence to all or a portion of a tracr mate sequence that is operably linked to the guide sequence. 
     The nucleic acid molecule encoding a Cas is advantageously codon optimized Cas. An example of a codon optimized sequence, is in this instance a sequence optimized for expression in a eukaryote, e.g., humans (i.e. being optimized for expression in humans), or for another eukaryote, animal or mammal as herein discussed; see, e.g., SaCas9 human codon optimized sequence in WO 2014/093622 (PCT/US2013/074667). Whilst this is preferred, it will be appreciated that other examples are possible and codon optimization for a host species other than human, or for codon optimization for specific organs is known. In some embodiments, an enzyme coding sequence encoding a Cas is codon optimized for expression in particular cells, such as eukaryotic cells. The eukaryotic cells may be those of or derived from a particular organism, such as a mammal, including but not limited to human, or non-human eukaryote or animal or mammal as herein discussed, e.g., mouse, rat, rabbit, dog, livestock, or non-human mammal or primate. In some embodiments, processes for modifying the germ line genetic identity of human beings and/or processes for modifying the genetic identity of animals which are likely to cause them suffering without any substantial medical benefit to man or animal, and also animals resulting from such processes, may be excluded. In general, codon optimization refers to a process of modifying a nucleic acid sequence for enhanced expression in the host cells of interest by replacing at least one codon (e.g. about or more than about 1, 2, 3, 4, 5, 10, 15, 20, 25, 50, or more codons) of the native sequence with codons that are more frequently or most frequently used in the genes of that host cell while maintaining the native amino acid sequence. Various species exhibit particular bias for certain codons of a particular amino acid. Codon bias (differences in codon usage between organisms) often correlates with the efficiency of translation of messenger RNA (mRNA), which is in turn believed to be dependent on, among other things, the properties of the codons being translated and the availability of particular transfer RNA (tRNA) molecules. The predominance of selected tRNAs in a cell is generally a reflection of the codons used most frequently in peptide synthesis. Accordingly, genes can be tailored for optimal gene expression in a given organism based on codon optimization. Codon usage tables are readily available, for example, at the “Codon Usage Database” available at www.kazusa.orjp/codon/and these tables can be adapted in a number of ways. See Nakamura, Y, et al. “Codon usage tabulated from the international DNA sequence databases: status for the year 2000” Nucl. Acids Res. 28:292 (2000). Computer algorithms for codon optimizing a particular sequence for expression in a particular host cell are also available, such as Gene Forge (Aptagen; Jacobus, Pa.), are also available. In some embodiments, one or more codons (e.g. 1, 2, 3, 4, 5, 10, 15, 20, 25, 50, or more, or all codons) in a sequence encoding a Cas correspond to the most frequently used codon for a particular amino acid. 
     In certain embodiments, the methods as described herein may comprise providing a Cas transgenic cell in which one or more nucleic acids encoding one or more guide RNAs are provided or introduced operably connected in the cell with a regulatory element comprising a promoter of one or more gene of interest. As used herein, the term “Cas transgenic cell” refers to a cell, such as a eukaryotic cell, in which a Cas gene has been genomically integrated. The nature, type, or origin of the cell are not particularly limiting according to the present invention. Also the way how the Cas transgene is introduced in the cell is may vary and can be any method as is known in the art. In certain embodiments, the Cas transgenic cell is obtained by introducing the Cas transgene in an isolated cell. In certain other embodiments, the Cas transgenic cell is obtained by isolating cells from a Cas transgenic organism. By means of example, and without limitation, the Cas transgenic cell as referred to herein may be derived from a Cas transgenic eukaryote, such as a Cas knock-in eukaryote. Reference is made to WO 2014/093622 (PCT/US13/74667), incorporated herein by reference. Methods of US Patent Publication Nos. 20120017290 and 20110265198 assigned to Sangamo BioSciences, Inc. directed to targeting the Rosa locus may be modified to utilize the CRISPR Cas system of the present invention. Methods of US Patent Publication No. 20130236946 assigned to Cellectis directed to targeting the Rosa locus may also be modified to utilize the CRISPR Cas system of the present invention. By means of further example reference is made to Platt et. al. (Cell; 159(2):440-455 (2014)), describing a Cas9 knock-in mouse, which is incorporated herein by reference. The Cas transgene can further comprise a Lox-Stop-polyA-Lox(LSL) cassette thereby rendering Cas expression inducible by Cre recombinase. Alternatively, the Cas transgenic cell may be obtained by introducing the Cas transgene in an isolated cell. Delivery systems for transgenes are well known in the art. By means of example, the Cas transgene may be delivered in for instance eukaryotic cell by means of vector (e.g., AAV, adenovirus, lentivirus) and/or particle and/or nanoparticle delivery, as also described herein elsewhere. 
     It will be understood by the skilled person that the cell, such as the Cas transgenic cell, as referred to herein may comprise further genomic alterations besides having an integrated Cas gene or the mutations arising from the sequence specific action of Cas when complexed with RNA capable of guiding Cas to a target locus, such as for instance one or more oncogenic mutations, as for instance and without limitation described in Platt et al. (2014), Chen et al., (2014) or Kumar et al. (2009). 
     In some embodiments, the Cas sequence is fused to one or more nuclear localization sequences (NLSs), such as about or more than about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more NLSs. In some embodiments, the Cas comprises about or more than about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more NLSs at or near the amino-terminus, about or more than about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more NLSs at or near the carboxy-terminus, or a combination of these (e.g. zero or at least one or more NLS at the amino-terminus and zero or at one or more NLS at the carboxy terminus). When more than one NLS is present, each may be selected independently of the others, such that a single NLS may be present in more than one copy and/or in combination with one or more other NLSs present in one or more copies. In a preferred embodiment of the invention, the Cas comprises at most 6 NLSs. In some embodiments, an NLS is considered near the N- or C-terminus when the nearest amino acid of the NLS is within about 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 40, 50, or more amino acids along the polypeptide chain from the N- or C-terminus. Non-limiting examples of NLSs include an NLS sequence derived from: the NLS of the SV40 virus large T-antigen, having the amino acid sequence PKKKRKV(SEQ ID NO: X); the NLS from nucleoplasmin (e.g. the nucleoplasmin bipartite NLS with the sequence KRPAATKKAGQAKKKK) (SEQ ID NO: X); the c-myc NLS having the amino acid sequence PAAKRVKLD (SEQ ID NO: X) or RQRRNELKRSP(SEQ ID NO: X); the hRNPA1 M9 NLS having the sequence NQSSNFGPMKGGNFGGRSSGPYGGGGQYFAKPRNQGGY(SEQ ID NO: X); the sequence RMRIZFKNKGKDTAELRRRRVEVSVELRKAKKDEQILKRRNV (SEQ ID NO: X) of the IBB domain from importin-alpha; the sequences VSRKRPRP (SEQ ID NO: X) and PPKKARED (SEQ ID NO: X) of the myoma T protein; the sequence POPKKKPL (SEQ ID NO: X) of human p53; the sequence SALIKKKKKMAP (SEQ ID NO: X) of mouse c-abl IV; the sequences DRLRR (SEQ ID NO: X) and PKQKKRK (SEQ ID NO: X) of the influenza virus NS1; the sequence RKLKKKIKKL (SEQ ID NO: X) of the Hepatitis virus delta antigen; the sequence REKKKFLKRR (SEQ ID NO: X) of the mouse Mx1 protein; the sequence KRKGDEVDGVDEVAKKKSKK (SEQ ID NO: X) of the human poly(ADP-ribose) polymerase; and the sequence RKCLQAGMNLEARKTKK (SEQ ID NO: X) of the steroid hormone receptors (human) glucocorticoid. In general, the one or more NLSs are of sufficient strength to drive accumulation of the Cas in a detectable amount in the nucleus of a eukaryotic cell. In general, strength of nuclear localization activity may derive from the number of NLSs in the Cas, the particular NLS(s) used, or a combination of these factors. Detection of accumulation in the nucleus may be performed by any suitable technique. For example, a detectable marker may be fused to the Cas, such that location within a cell may be visualized, such as in combination with a means for detecting the location of the nucleus (e.g. a stain specific for the nucleus such as DAPI). Cell nuclei may also be isolated from cells, the contents of which may then be analyzed by any suitable process for detecting protein, such as immunohistochemistry, Western blot, or enzyme activity assay. Accumulation in the nucleus may also be determined indirectly, such as by an assay for the effect of CRISPR complex formation (e.g. assay for DNA cleavage or mutation at the target sequence, or assay for altered gene expression activity affected by CRISPR complex formation and/or Cas enzyme activity), as compared to a control no exposed to the Cas or complex, or exposed to a Cas lacking the one or more NLSs. 
     In certain aspects the invention involves vectors, e.g. for delivering or introducing in a cell Cas and/or RNA capable of guiding Cas to a target locus (i.e. guide RNA), but also for propagating these components (e.g. in prokaryotic cells). A used herein, a “vector” is a tool that allows or facilitates the transfer of an entity from one environment to another. It is a replicon, such as a plasmid, phage, or cosmid, into which another DNA segment may be inserted so as to bring about the replication of the inserted segment. Generally, a vector is capable of replication when associated with the proper control elements. In general, the term “vector” refers to a nucleic acid molecule capable of transporting another nucleic acid to which it has been linked. Vectors include, but are not limited to, nucleic acid molecules that are single-stranded, double-stranded, or partially double-stranded; nucleic acid molecules that comprise one or more free ends, no free ends (e.g. circular); nucleic acid molecules that comprise DNA, RNA, or both; and other varieties of polynucleotides known in the art. One type of vector is a “plasmid,” which refers to a circular double stranded DNA loop into which additional DNA segments can be inserted, such as by standard molecular cloning techniques. Another type of vector is a viral vector, wherein virally-derived DNA or RNA sequences are present in the vector for packaging into a virus (e.g. retroviruses, replication defective retroviruses, adenoviruses, replication defective adenoviruses, and adeno-associated viruses (AAVs)). Viral vectors also include polynucleotides carried by a virus for transfection into a host cell. Certain vectors are capable of autonomous replication in a host cell into which they are introduced (e.g. bacterial vectors having a bacterial origin of replication and episomal mammalian vectors). Other vectors (e.g., non-episomal mammalian vectors) are integrated into the genome of a host cell upon introduction into the host cell, and thereby are replicated along with the host genome. Moreover, certain vectors are capable of directing the expression of genes to which they are operatively-linked. Such vectors are referred to herein as “expression vectors.” Common expression vectors of utility in recombinant DNA techniques are often in the form of plasmids. 
     Recombinant expression vectors can comprise a nucleic acid of the invention in a form suitable for expression of the nucleic acid in a host cell, which means that the recombinant expression vectors include one or more regulatory elements, which may be selected on the basis of the host cells to be used for expression, that is operatively-linked to the nucleic acid sequence to be expressed. Within a recombinant expression vector, “operably linked” is intended to mean that the nucleotide sequence of interest is linked to the regulatory element(s) in a manner that allows for expression of the nucleotide sequence (e.g. in an in vitro transcription/translation system or in a host cell when the vector is introduced into the host cell). With regards to recombination and cloning methods, mention is made of U.S. patent application Ser. No. 10/815,730, published Sep. 2, 2004 as US 2004-0171156 A1, the contents of which are herein incorporated by reference in their entirety. 
     The vector(s) can include the regulatory element(s), e.g., promoter(s). The vector(s) can comprise Cas encoding sequences, and/or a single, but possibly also can comprise at least 3 or 8 or 16 or 32 or 48 or 50 guide RNA(s) (e.g., sgRNAs) encoding sequences, such as 1-2, 1-3, 1-4 1-5, 3-6, 3-7, 3-8, 3-9, 3-10, 3-8, 3-16, 3-30, 3-32, 3-48, 3-50 RNA(s) (e.g., sgRNAs). In a single vector there can be a promoter for each RNA (e.g., sgRNA), advantageously when there are up to about 16 RNA(s) (e.g., sgRNAs); and, when a single vector provides for more than 16 RNA(s) (e.g., sgRNAs), one or more promoter(s) can drive expression of more than one of the RNA(s) (e.g., sgRNAs), e.g., when there are 32 RNA(s) (e.g., sgRNAs), each promoter can drive expression of two RNA(s) (e.g., sgRNAs), and when there are 48 RNA(s) (e.g., sgRNAs), each promoter can drive expression of three RNA(s) (e.g., sgRNAs). By simple arithmetic and well established cloning protocols and the teachings in this disclosure one skilled in the art can readily practice the invention as to the RNA(s) (e.g., sgRNA(s) for a suitable exemplary vector such as AAV, and a suitable promoter such as the U6 promoter, e.g., U6-sgRNAs. For example, the packaging limit of AAV is ˜4.7 kb. The length of a single U6-sgRNA (plus restriction sites for cloning) is 361 bp. Therefore, the skilled person can readily fit about 12-16, e.g., 13 U6-sgRNA cassettes in a single vector. This can be assembled by any suitable means, such as a golden gate strategy used for TALE assembly (www.genome-engineering.org/taleffectors/). The skilled person can also use a tandem guide strategy to increase the number of U6-sgRNAs by approximately 1.5 times, e.g., to increase from 12-16, e.g., 13 to approximately 18-24, e.g., about 19 U6-sgRNAs. Therefore, one skilled in the art can readily reach approximately 18-24, e.g., about 19 promoter-RNAs, e.g., U6-sgRNAs in a single vector, e.g., an AAV vector. A further means for increasing the number of promoters and RNAs, e.g., sgRNA(s) in a vector is to use a single promoter (e.g., U6) to express an array of RNAs, e.g., sgRNAs separated by cleavable sequences. And an even further means for increasing the number of promoter-RNAs, e.g., sgRNAs in a vector, is to express an array of promoter-RNAs, e.g., sgRNAs separated by cleavable sequences in the intron of a coding sequence or gene; and, in this instance it is advantageous to use a polymerase II promoter, which can have increased expression and enable the transcription of long RNA in a tissue specific manner. (see, e.g., nar.oxfordjournals.org/content/34/7/e53. short, www.nature.com/mt/journal/v16/n9/abs/mt2008144a.html). In an advantageous embodiment, AAV may package U6 tandem sgRNA targeting up to about 50 genes. Accordingly, from the knowledge in the art and the teachings in this disclosure the skilled person can readily make and use vector(s), e.g., a single vector, expressing multiple RNAs or guides or sgRNAs under the control or operatively or functionally linked to one or more promoters—especially as to the numbers of RNAs or guides or sgRNAs discussed herein, without any undue experimentation. 
     The guide RNA(s), e.g., sgRNA(s) encoding sequences and/or Cas encoding sequences, can be functionally or operatively linked to regulatory element(s) and hence the regulatory element(s) drive expression. The promoter(s) can be constitutive promoter(s) and/or conditional promoter(s) and/or inducible promoter(s) and/or tissue specific promoter(s). The promoter can be selected from the group consisting of RNA polymerases, pol I, pol II, pol III, T7, U6, H1, retroviral Rous sarcoma virus (RSV) LTR promoter, the cytomegalovirus (CMV) promoter, the SV40 promoter, the dihydrofolate reductase promoter, the β-actin promoter, the phosphoglycerol kinase (PGK) promoter, and the EF1α promoter. An advantageous promoter is the promoter is U6. 
     Ways to package Cas coding nucleic acid molecules, e.g., DNA, into vectors, e.g., viral vectors, to mediate genome modification in vivo include:
         To achieve NHEJ-mediated gene knockout:
           Single virus vector:
               Vector containing two or more expression cassettes:   Promoter-Cas coding nucleic acid molecule -terminator   Promoter-gRNA1-terminator   Promoter-gRNA2-terminator   Promoter-gRNA(N)-terminator (up to size limit of vector)   
               Double virus vector:
               Vector 1 containing one expression cassette for driving the expression of Cas   Promoter-Cas coding nucleic acid molecule-terminator   Vector 2 containing one more expression cassettes for driving the expression of one or more guideRNAs   Promoter-gRNA1-terminator   Promoter-gRNA(N)-terminator (up to size limit of vector)   
               
           To mediate homology-directed repair.       

     In addition to the single and double virus vector approaches described above, an additional vector is used to deliver a homology-direct repair template. 
     The promoter used to drive Cas coding nucleic acid molecule expression can include: 
     AAV ITR can serve as a promoter: this is advantageous for eliminating the need for an additional promoter element (which can take up space in the vector). The additional space freed up can be used to drive the expression of additional elements (gRNA, etc.). Also, ITR activity is relatively weaker, so can be used to reduce potential toxicity due to over expression of Cas. 
     For ubiquitous expression, can use promoters: CMV, CAG, CBh, PGK, SV40, Ferritin heavy or light chains, etc. 
     For brain or other CNS expression, can use promoters: SynapsinI for all neurons, CaMKIIalpha for excitatory neurons, GAD67 or GAD65 or VGAT for GABAergic neurons, etc. 
     For liver expression, can use Albumin promoter. 
     For lung expression, can use SP-B. 
     For endothelial cells, can use ICAM. 
     For hematopoietic cells can use IFNbeta or CD45. 
     For Osteoblasts can use OG-2. 
     The promoter used to drive guide RNA can include: 
     Pol III promoters such as U6 or H1 
     Use of Pol II promoter and intronic cassettes to express gRNA 
     WORKING EXAMPLES 
     Example 1—Computational Pipeline for the Discovery of Class 2 CRISPR-Cas Systems from Genomic and Metagenomic Sequences 
     A pipeline that was developed for systematic detection of Class 2 CRISPR-Cas systems is shown in  FIG. 1 . The procedure begins with the identification of an ‘seed’ that signifies the presence of a CRISPR-Cas locus in a given nucleotide sequence. In the previously reported analysis, we used as the seed Cas1, the Cas protein that is most common in CRISPR-Cas systems and is most highly conserved at the sequence level. To ensure maximum sensitivity of detection, the search was performed by comparing a Cas1 sequence profile to translated genomic and metagenomic sequences. After the cas1 genes were detected, the neighborhoods were examined for the presence of other cas genes by searching with approximately 400 previously developed profiles for Cas proteins and applying the criteria for the classification of the CRISPR-cas loci. All loci that were assigned to known CRISPR-Cas subtypes by this procedure were discarded from the subsequent analysis. Among the remaining cas1 neighborhoods, those encoding large proteins (&gt;500 amino acids) were chosen for detailed analysis under the premise that Cas9 and Cpf1 are large proteins (typically, &gt;1000 aa), and the respective protein structures suggest that this large size is a requirement to accommodate the complex of the crRNA with the target DNA. The sequences of such large proteins were then screened for known protein domains using sensitive profile-based methods such as HHpred, secondary structure prediction and manual examination of multiple alignments. The proteins containing domains deemed irrelevant in the context of the CRISPR-Cas function (e.g. membrane transporters) were discarded. The use of maximally sensitive methods at this stage is essential because proteins involved in antivirus defense typically evolve extremely fast. This implementation of the pipeline led to the discovery of two subtype of type V (effectors contain a RuvC-like nuclease domains distantly related to that of Cas9) and the new type VI (putative effector contains two HEPN domains). To expand the search to non-autonomous CRISPR-Cas systems, we repeated the same procedures with the CRISPR array used as the seed. The second run of the pipeline resulted in the detection of an additional, heterogeneous subtype of putative type V systems and two subtypes of type VI. The setup of the search described here (see  FIG. 1 ) whereby all large proteins encoded near a cas1 gene or a CRISPR array were analyzed in detail implies that the detected variants represent the complete diversity of CRISPR-Cas systems detectable in the currently available genomes. 
     Example 2—Putative Type V System 
     The distinctive feature of type V CRISPR-Cas sequence is the presence, in the multidomain effector proteins, of RuvC-like nucleases domain. The type II systems share this domain but additionally possess the inserted HNH nuclease domain ( FIG. 2 ). Other than the RuvC-like domain, the effector proteins of the four type V subtypes do not share any detectable sequence similarity to each other or to the Cas9 effectors of type II. However, the comparison of the two available Class 2 effector crystal structures, those of Cas9 and Cpf1, reveals a common structural framework. Both proteins form generally similar bilobed structures in which the RECognition (REC) and NUClease (NUC) lobes are joined through the positively charged bridge helix. Moreover, Cas9 and Cpf1 contain similarly (although not identically) positioned but unrelated domains inserted into the RuvC domain and responsible for the target strand cleavage. The structures of other (putative) large type V effectors discovered in complete CRISPR-Cas loci (i.e., by running the pipeline with the Cas1 seed) are not yet available but a robust interference activity has been demonstrated for subtype V-B. All these effectors share similar size and a single common domain, the RuvC-like endonuclease, although the actual sequence similarity between the effector proteins of different subtypes is extremely low. It appears likely that the type V effectors adopt similar bilobed structures that are required to hold together the crRNA and the target DNA although the effector proteins of different subtypes do not appear to be directly related. 
     Indeed, the search for likely ancestors of the type II and type V effectors showed that the RuvC-like nuclease domains are related to TnpB proteins, extremely abundant but poorly functionally characterized nucleases encoded by numerous autonomous and non-autonomous bacterial and archaeal transposons. In addition to the RuvC-like nuclease domain, the TnpB proteins contain a counterpart to the arginine-rich bridge helix suggesting the possibility that the TnpB protein bind RNA. For Cas9, the “smoking gun”, the likely direct ancestor of the type II effectors, has been identified on the basis of highly significant sequence similarity and the presence of the HNH insert in the RuvC-like nuclease domain of a distinct family of TnpB proteins that has been denoted IscB (Insertion Sequences Cas9-like protein B). For the effector proteins of type V, the direct ancestry is difficult to identify given that the similarity between these proteins and TnpB is much lower than it is in the case of Cas9 and is largely limited to the RuvC-like nuclease catalytic motifs. Nevertheless, the effectors of the three subtypes of type V clearly show the highest similarity to different TnpB families leading to the hypothesis of independent origins of the type V effectors from the pool of tnpB genes. It has been proposed that the respective TnpB-encoding transposons initially integrated in the vicinity of an adaptation module and a CRISPR array, possibly displacing Class 1 effector modules. Such a scenario is compatible with the observations that the cas1 genes of different Class 2 subtypes are nested with different branches of Class 1. 
     The search for putative CRISPR-cas loci lacking the adaptation module (i.e. with a CRISPR used as the seed; see  FIG. 1 ) yielded several additional variants of putative type V systems ( FIG. 2 ) that might shed light on the evolutionary path from TnpB to full-fledged CRISPR-cas effectors. These proteins that we provisionally assigned to subtype V-U share two features that clearly distinguish them from the type II and type V effectors associated with complete CRISPR-cas loci. First, these proteins are much smaller than the effectors of complete Class2 systems, comprising between ca. 400 (the typical size of TnpB) and ca. 700 amino acids (roughly between the size of TnpB and the typical size of the bona fide Class 2 effectors). Second, these smaller TnpB homologs associated with CRISPR arrays show a much higher level of similarity to TnpB than the larger type I and type V effectors. In particular, 5 groups of these smaller TnpB homologs showed evolutionary coherence in terms of sequence conservation and consistent association with CRISPR arrays ( FIG. 2 ). In view of the identification of these smaller CRISPR-associated TnpB homologs, we ran the pipeline ( FIG. 1 ) in a modified form whereby the requirement for the minimal length of the protein adjacent to the CRISPR-array was lifted. The results were specifically searched for the presence of additional TnpB homologs. This analysis led to the detection of many CRISPR-associated TnpB homologs in the size range typical of the transposon-encoded TnpB, i.e. about 400 amino acids. 
     Whereas for the larger type V effectors, low sequence conservation precluded reliable phylogenetic analysis, a robust tree could be constructed for the smaller CRISPR-associated homologs and the typical TnpB. The topology of this tree clearly indicated that 4 of the 5 distinct variants of subtype V-U (hereinafter V-U1-5) originated from different TnpB families ( FIG. 4 ), in agreement with the hypothesis on the independent evolution of the effectors of different Class 2 variants (subtypes) from transposon-encoded nucleases. In addition, a fifth group (V-U5) that is represented in a variety of Cyanobacteria consists of diverged TnpB homologs with multiple mutations in the catalytic motifs of the RuvC-like domain and was accordingly not included in the phylogeny. Of these 5 distinct variants, V-U1 is represented in diverse bacteria whereas the remaining ones are largely limited in their spread to a particular bacterial taxon ( FIGS. 4 and 5 ). We further extended this evolutionary analysis to all (putative) type V effectors by building a cluster dendrogram based on the distances derived from profile to profile comparisons of the respective protein sequences. The results support the possibility that the effectors of each of the identified subtypes as well as several variants within the subtype V-U originated independently from different TnpB families. 
     The subtype V-U TnpB-like proteins appear to be too small to adopt the bilobed structure of sufficient size to accommodate the complex of the crRNA with the target DNA as the typical Class 2 effectors do, and therefore are unlikely to function in that capacity, at least not without additional partners. Nevertheless, the evolutionarily stable association of at least 5 distinct variants with CRISPR arrays implies that at least some of these proteins do perform CRISPR-dependent biological functions. Such functions might involve a typical CRISPR response aided by additional, non-Cas proteins. Remarkably, the CRISPR arrays associated with group V-U3 that is represented primarily in  Bacilli  and  Clostridia  contain multiple spacers that exactly match genomic sequences of bacteriophages infecting these bacteria. The presence of the phage-specific spacers implies that at least this variant within subtype V-U is a functional CRISPR-Cas system that is actively engaged in anti-phage adaptive immunity. The complete genomes containing the V-U3 (as well as V-U4) loci typically lack additional CRISPR-Cas systems. Alternatively, some of the V-U systems might be involved in distinct regulatory roles. This is particularly plausible for the V-U5 variant which appears to encompass a catalytically inactive TnpB homolog ( FIG. 2 ). It is furthermore notable that in the complete genomes that contain the V-U2 and V-U5 loci along with other CRISPR-Cas systems, the CRISPR sequences associated with the former loci are unique, suggestive of distinct functions for these putative type V loci. 
     The locus architectures of the type V CRISPR-Cas systems are comparatively simple and resemble those of the type II loci ( FIG. 2 ). Among the complete loci, subtype V-C is characterized by the simplest organization among the known systems, with the putative adaptation module consisting only of a distinct variety of Cas1 but no Cas2 protein. Subtypes V-A and V-B share the composition of the adaptation module that, in addition to Cas1 and Cas2, includes the Cas4 nuclease that in subtype V-B is encoded by a fusion gene with Cas1 ( FIG. 2 ); the role of Cas4 in adaptation has been demonstrated for some type I systems. The subtype I-U loci lack any additional cas genes ( FIG. 2 ). An important difference between the subtypes of type V is the requirement or lack thereof for a tracrRNA. Similar to type II, the type V-B systems have been shown to encode a tracrRNA. In contrast, Cpf1, the subtype V-A effector, has been characterized as a single RNA-guided nuclease that does not depend on tracrRNA which indeed does not appear to be encoded in the subtype V-A loci. 
     Newly discovered type V-U effectors are listed in Table 1. Multiple alignment of representative effectors from each of the five V-U subtypes are provided in  FIG. 9 . 
     
       
         
           
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Type V-U CRISPR Effectors 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 SEQ 
                   
                   
                 Genome 
                 Coordinates of 
               
               
                 ID No 
                 Local ID 
                 Subfamily 
                 partition ID 
                 the gene 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 1 
                 118577413 
                 V-U1 
                 Pelobacter_propionicus_DSM_2379_uid58255 
                 NC_008607 
                 189989 . . . 191983 
               
               
                 2 
                 1096423661 
                 V-U1 
                 Mycobacterium conceptionense 
                 LSKA01000495.1 
                 6173 . . . 7963 
               
               
                 3 
                 1024922355 
                 V-U1 
                 Gordonia otitidis NBRC 100426 
                 CP003591.1 
                 3406549 . . . 3408810 
               
               
                 4 
                 1903609002 
                 V-U1 
                 Mycobacterium mucogenicum 
                 CP013015.1 
                 1046310 . . . 1047626 
               
               
                   
                   
                   
                 strain CCH10-A2 CCH10-A2_contig531 
               
               
                 5 
                 1003450287 
                 V-U1 
                 Meiothermus silvanus DSM 9946 
                 CP004310.1 
                 7869 . . . 9053 
               
               
                 6 
                 1507071745 
                 V-U1 
                 Clostridiales bacterium DRI-13 
                 JHDU01000036.1 
                 5392 . . . 6912 
               
               
                   
                   
                   
                 BR63DRAFT_scaffold00024.24_C 
               
               
                 7 
                 218248844 
                 V-U2 
                 Cyanothece_PCC_8801_uid59027 
                 NC_011726 
                 4331770 . . . 4333254 
               
               
                 8 
                 428311397 
                 V-U2 
                 Microcoleus_PCC_7113_uid183114 
                 NC_019738 
                 3704312 . . . 3706207 
               
               
                 9 
                 1046552329 
                 V-U2 
                 Lyngbya aestuarii BL J 
                 GG704699.1 
                 234671 . . . 235915 
               
               
                 10 
                 1019491369 
                 V-U2 
                 Lyngbya sp. PCC 8106 
                 CP001701.1 
                 2289597 . . . 2291435 
               
               
                 11 
                 1002782830 
                 V-U2 
                 Cyanothece sp. PCC 8802 
                 CM000744.1 
                 5384706 . . . 5386142 
               
               
                 12 
                 1030942420 
                 V-U2 
                 Microcystis aeruginosa PCC 9432 
                 AOLW01000047.1 
                 195031 . . . 196203 
               
               
                 13 
                 1305565200 
                 V-U2 
                 Dolichospermum circinale 
                 JVFS01000043.1 
                 149459 . . . 151135 
               
               
                   
                   
                   
                 AWQC310F genomic scaffold 
               
               
                   
                   
                   
                 310F_Scaffold21 
               
               
                 14 
                 402558454 
                 V-U3 
                 Bacillus_thuringiensis_HD_771_uid173374 
                 NC_018501 
                 43675 . . . 45027 
               
               
                 15 
                 300853273 
                 V-U3 
                 Clostridium_ljungdahlii_DSM_13528_uid50583 
                 NC_014328 
                 47093 . . . 48508 
               
               
                 16 
                 488769073 
                 V-U3 
                 Clostridium_pasteurianum_BC1_uid201478 
                 NC_021182 
                 86649 . . . 87935 
               
               
                 17 
                 317133985 
                 V-U3 
                 Ruminococcus_albus_7_uid51721 
                 NC_014824 
                 316073 . . . 317434 
               
               
                 18 
                 1705264553 
                 V-U3 
                 Clostridium botulinum strain 
                 CP000239.1 
                 731379 . . . 732659 
               
               
                   
                   
                   
                 713_CBOT 382_89760_1793432 
               
               
                 19 
                 1043743222 
                 V-U3 
                 Peptoclostridium difficile P20 
                 AWWH01000158.1 
                 23337 . . . 24521 
               
               
                 20 
                 1043409625 
                 V-U3 
                 Peptoclostridium difficile 
                 LN851177.1 
                 607439 . . . 608656 
               
               
                   
                   
                   
                 DA00114 
               
               
                 21 
                 1017733463 
                 V-U3 
                 Clostridium hiranonis DSM 13275 
                 CP001293.1 
                 171333 . . . 172478 
               
               
                 22 
                 1804030309 
                 V-U3 
                 Cellulosilyticum ruminicola JCM 
                 JH930358.1 
                 842544 . . . 844580 
               
               
                   
                   
                   
                 14822 DNA 
               
               
                 23 
                 1077873159 
                 V-U3 
                 Clostridium novyi B str. NCTC 
                 AAVU01000008.1 
                 88984 . . . 90171 
               
               
                   
                   
                   
                 9691 
               
               
                 24 
                 1905047130 
                 V-U3 
                 Clostridium botulinum strain 
                 KI543234.1 
                  99381 . . . 100637 
               
               
                   
                   
                   
                 AM1195 AM1195_7 
               
               
                 25 
                 1018643584 
                 V-U3 
                 Bacillus mycoides Rock3-17 
                 CP001287.1 
                 3090392 . . . 3092440 
               
               
                 26 
                 1029128199 
                 V-U3 
                 Bacillus cereus MC67 
                 AP014821.1 
                 690780 . . . 692630 
               
               
                 27 
                 1059072407 
                 V-U3 
                 Ruminococcus albus SY3 
                 AP017308.1 
                 3158482 . . . 3159606 
               
               
                 28 
                 1017485595 
                 V-U3 
                 Eubacterium siraeum DSM 15702 
                 AAXW01000027.1 
                 13366 . . . 15204 
               
               
                 29 
                 1077873155 
                 V-U3 
                 Clostridium novyi B str. NCTC 
                 AAVU01000010.1 
                 146528 . . . 147619 
               
               
                   
                   
                   
                 9691 
               
               
                 30 
                 1100000271 
                 V-U3 
                 Thermincola ferriacetica 
                 KK307111.1 
                 94260 . . . 95639 
               
               
                 31 
                 1804024535 
                 V-U3 
                 Syntrophomonas palmitatica JCM 
                 JH930357.1 
                 752813 . . . 753934 
               
               
                   
                   
                   
                 14374 DNA 
               
               
                 32 
                 1122605119 
                 V-U3 
                 Bacillus cereus 
                 AP017295.1 
                 5092456 . . . 5094363 
               
               
                 33 
                 1019720777 
                 V-U3 
                 Bacillus cereus H3081.97 
                 GL892032.1 
                 2978305 . . . 2979429 
               
               
                 34 
                 1700567090 
                 V-U3 
                 Bacillus cereus strain Lr 2-Apr 
                 CP000240.1 
                 605551 . . . 606744 
               
               
                   
                   
                   
                 LG48_098 
               
               
                 35 
                 529067778 
                 V-U4 
                 Corynebacterium_maris_DSM_45190_uid214081 
                 NC_021920 
                 4967 . . . 6613 
               
               
                 36 
                 433644734 
                 V-U4 
                 Mycobacterium_smegmatis_JS623_uid184820 
                 NC_019959 
                 39760 . . . 41247 
               
               
                 37 
                 451770599 
                 V-U4 
                 Mycobacterium_yongonense_05_1390_uid189649 
                 NC_020276 
                 1603 . . . 3144 
               
               
                 38 
                 1706842133 
                 V-U4 
                 Micrococcus luteus strain 
                 LGTE01000024.1 
                 35698 . . . 37032 
               
               
                   
                   
                   
                 773_MLUT 184_13961_611621 
               
               
                 39 
                 1009979974 
                 V-U4 
                 Corynebacterium glutamicum 
                 LGVS01000034.1 
                 22840 . . . 24252 
               
               
                 40 
                 1016662850 
                 V-U4 
                 Rothia dentocariosa M567 
                 KB899040.1 
                 1248881 . . . 1250119 
               
               
                 41 
                 1705782714 
                 V-U4 
                 Rothia mucilaginosa strain 
                 BBCE01000017.1 
                 52764 . . . 54257 
               
               
                   
                   
                   
                 1211_RMUC 
               
               
                   
                   
                   
                 305_65084_1729696_109 —   
               
               
                 42 
                 1800346325 
                 V-U4 
                 Streptococcus parasanguinis 
                 JQLJ01000001.1 
                 1862742 . . . 1863920 
               
               
                   
                   
                   
                 strain 348_SPAR 
               
               
                   
                   
                   
                 455_33078_318375 
               
               
                 43 
                 1706614983 
                 V-U4 
                 Rothia mucilaginosa strain 
                 LGTE01000024.1 
                 32013 . . . 33293 
               
               
                   
                   
                   
                 473_RMUC 
               
               
                   
                   
                   
                 364_156967_2761259_266 —   
               
               
                 44 
                 1206162758 
                 V-U4 
                 Cellulosimicrobium cellulans LMG 
                 AVIV01000129.1 
                 1206 . . . 2411 
               
               
                   
                   
                   
                 16121 WGS project 
               
               
                   
                   
                   
                 CAOI00000000 data 
               
               
                 45 
                 1095979361 
                 V-U4 
                 Streptomyces regensis 
                 LFOD01000003.1 
                 204245 . . . 206056 
               
               
                 46 
                 1305448890 
                 V-U4 
                 Streptomyces sp. CNS606 
                 JVYQ01000016.1 
                 47267 . . . 48940 
               
               
                   
                   
                   
                 K304DRAFT_scaffold00043.43_C 
               
               
                 47 
                 1017562432 
                 V-U4 
                 Streptomyces sp. SPB74 
                 CP001291.1 
                 871333 . . . 872835 
               
               
                 48 
                 1075489406 
                 V-U4 
                 Streptomyces wadayamensis 
                 AAVU01000062.1 
                 13590 . . . 15629 
               
               
                 49 
                 1504922986 
                 V-U4 
                 Streptomyces rimosus subsp. 
                 GG770539.1 
                 3044316 . . . 3045845 
               
               
                   
                   
                   
                 rimosus strain NRRL WC-3927 
               
               
                   
                   
                   
                 contig19.1 
               
               
                 50 
                 1075265077 
                 V-U4 
                 Kitasatospora cheerisanensis 
                 LATL02000229.1 
                 28651 . . . 29838 
               
               
                   
                   
                   
                 KCTC 2395 
               
               
                 51 
                 1207200189 
                 V-U4 
                 Nocardiopsis synnemataformans 
                 JYNK01000007.1 
                 551994 . . . 553157 
               
               
                   
                   
                   
                 DSM 44143 contig_9 
               
               
                 52 
                 1207283968 
                 V-U4 
                 Nocardiopsis alba DSM 43377 
                 KE150269.1 
                 1355683 . . . 1357281 
               
               
                   
                   
                   
                 contig_18 
               
               
                 53 
                 1048804328 
                 V-U4 
                 Streptomyces niveus NCIMB 
                 CP002427.1 
                 482416 . . . 483669 
               
               
                   
                   
                   
                 11891 
               
               
                 54 
                 1401235120 
                 V-U4 
                 Mycobacterium sp. UM_RHS 
                 KK073768.1 
                 4862951 . . . 4864153 
               
               
                   
                   
                   
                 Contig_9 
               
               
                 55 
                 1040961339 
                 V-U4 
                 Propionimicrobium 
                 KK853997.1 
                 2723615 . . . 2725093 
               
               
                   
                   
                   
                 lymphophilum ACS-093-V-SCH5 
               
               
                 56 
                 1405224212 
                 V-U4 
                 Streptomyces sp. CNH099 
                 JH980292.1 
                 654051 . . . 655259 
               
               
                   
                   
                   
                 B121DRAFT_scaffold_35.36_C 
               
               
                 57 
                 440680311 
                 V-U5 
                 Anabaena cylindrica PCC 7122 
                 NC_019771 
                 736937 . . . 738865 
               
               
                 58 
                 428305730 
                 V-U5 
                 Crinalium epipsammum PCC 
                 NC_019753 
                 2459484 . . . 2461619 
               
               
                   
                   
                   
                 9333 
               
               
                 59 
                 428306136 
                 V-U5 
                 Crinalium epipsammum PCC 
                 NC_019753 
                 2911658 . . . 2913502 
               
               
                   
                   
                   
                 9333 
               
               
                 60 
                 220908491 
                 V-U5 
                 Cyanothece sp. PCC 7425 
                 NC_011884 
                 3086956 . . . 3088887 
               
               
                 61 
                 257060041 
                 V-U5 
                 Cyanothece sp. PCC 8802 
                 NC_013161 
                 2226229 . . . 2228232 
               
               
                 62 
                 428776047 
                 V-U5 
                 Halothece sp. PCC 7418 
                 NC_019779 
                 1563969 . . . 1565936 
               
               
                 63 
                 428311644 
                 V-U5 
                 Microcoleus sp. PCC 7113 
                 NC_019738 
                 4021458 . . . 4023371 
               
               
                 64 
                 428312908 
                 V-U5 
                 Microcoleus sp. PCC 7113 
                 NC_019738 
                 5618464 . . . 5620371 
               
               
                 65 
                 17230183 
                 V-U5 
                 Nostoc sp. PCC 7120 
                 NC_003272 
                 3282086 . . . 3284110 
               
               
                 66 
                 1019531886 
                 V-U5 
                 Cyanothece sp. CCY0110 
                 AEIQ01000064.1 
                  599 . . . 2212 
               
               
                 67 
                 1111222001 
                 V-U5 
                 Mastigocoleus testarum BC008 
                 ANAW01000009.1 
                 89276 . . . 90784 
               
               
                 68 
                 1406824382 
                 V-U5 
                 Tolypothrix Scytonema hofmanni 
                 AUFD01000045.1 
                 6273 . . . 7820 
               
               
                   
                   
                   
                 UTEX 2349 genomic scaffold 
               
               
                   
                   
                   
                 Tol9009DRAFT_TPD.8 
               
               
                 69 
                 1206817639 
                 V-U5 
                 Calothrix sp. PCC 7103 genomic 
                 AVLX01000025.1 
                 5639 . . . 6853 
               
               
                   
                   
                   
                 scaffold Cal7103DRAFT_CPM.1 
               
               
                 70 
                 1007109870 
                 V-U5 
                 Anabaena cylindrica PCC 7122 
                 AYKZ01000007.1 
                 13194 . . . 14723 
               
               
                 71 
                 1300380544 
                 V-U5 
                 Scytonema hofmanni PCC 7110 
                 AZVL01000034.1 
                 4057 . . . 5586 
               
               
                   
                   
                   
                 contig00008 
               
               
                 72 
                 1002400088 
                 V-U5 
                 Cyanothece sp. PCC 8801 
                 BARH01000009.1 
                 169965 . . . 171089 
               
               
                 73 
                 1007062327 
                 V-U5 
                 Calothrix sp. PCC 6303 
                 BBCG01000021.1 
                 37618 . . . 38814 
               
               
                 74 
                 1002125473 
                 V-U5 
                 Nostoc punctiforme PCC 73102 
                 CP000117.1 
                 2724972 . . . 2726903 
               
               
                 75 
                 1205733553 
                 V-U5 
                 Nodosilinea nodulosa PCC 7104 
                 CP001037.1 
                 6984000 . . . 6985919 
               
               
                   
                   
                   
                 genomic scaffold 
               
               
                   
                   
                   
                 Lepto7104DRAFT_LPD.2 
               
               
                 76 
                 1507700957 
                 V-U5 
                 Myxosarcina sp. GI1 contig_23 
                 CP001403.1 
                 703203 . . . 704498 
               
               
                 77 
                 1000428792 
                 V-U5 
                 Nostoc sp. PCC 7120 
                 CP001785.1 
                 691337 . . . 692632 
               
               
                 78 
                 1085030414 
                 V-U5 
                 Scytonema millei VB511283 
                 CP002044.1 
                 109533 . . . 111143 
               
               
                 79 
                 1007036557 
                 V-U5 
                 Geitlerinema sp. PCC 7407 
                 CP002408.1 
                 664453 . . . 665595 
               
               
                 80 
                 1004799941 
                 V-U5 
                 Anabaena variabilis ATCC 29413 
                 CP008811.1 
                 36391 . . . 37491 
               
               
                 81 
                 1085045623 
                 V-U5 
                 Lyngbya confervoides 
                 CP009520.1 
                 3546198 . . . 3547451 
               
               
                   
                   
                   
                 BDU141951 
               
               
                 82 
                 1030021203 
                 V-U5 
                 Tolypothrix sp. PCC 7601 
                 CP011832.1 
                 2453693 . . . 2454940 
               
               
                 83 
                 1016058386 
                 V-U5 
                 Nostoc sp. NIES-3756 
                 HG764817.1 
                 5979713 . . . 5981140 
               
               
                 84 
                 1016001624 
                 V-U5 
                 Geminocystis sp. NIES-3709 
                 JENV01000018.1 
                 78100 . . . 79593 
               
               
                 85 
                 1002781021 
                 V-U5 
                 Cyanothece sp. PCC 8802 
                 JH792114.1 
                 681985 . . . 683475 
               
               
                 86 
                 1085056708 
                 V-U5 
                 Hassallia byssoidea VB512170 
                 JQNS01000003.1 
                 410982 . . . 412205 
               
               
                 87 
                 1405885249 
                 V-U5 
                 Aphanizomenon flos-aquae NIES- 
                 JVKQ01000122.1 
                 24882 . . . 26570 
               
               
                   
                   
                   
                 81 genomic scaffold 
               
               
                   
                   
                   
                 scaffold00002 
               
               
                 88 
                 1004798910 
                 V-U5 
                 Anabaena variabilis ATCC 29413 
                 KB217483.1 
                 719459 . . . 721408 
               
               
                 89 
                 1002781834 
                 V-U5 
                 Cyanothece sp. PCC 8802 
                 KB976804.1 
                 107528 . . . 108649 
               
               
                 90 
                 1300485477 
                 V-U5 
                 Leptolyngbya boryana PCC 6306 
                 KE384066.1 
                 16736 . . . 17842 
               
               
                   
                   
                   
                 genomic scaffold 
               
               
                   
                   
                   
                 LepboDRAFT_LPC.1 
               
               
                 91 
                 1016002403 
                 V-U5 
                 Geminocystis sp. NIES-3709 
                 KQ956191.1 
                 3754 . . . 4848 
               
               
                 92 
                 1002400093 
                 V-U5 
                 Cyanothece sp. PCC 8801 
                 LIOK01000006.1 
                 162536 . . . 163630 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 SEQ 
                   
                   
               
               
                   
                 ID No 
                 Strand 
                 Organism 
               
               
                   
                   
               
               
                   
                 1 
                 − 
                 Pelobacter_propionicus_DSM_2379_uid58255 
               
               
                   
                 2 
                 + 
                 Mycobacterium_mucogenicum_CCH10_A2_GCA_001556905.1 
               
               
                   
                 3 
                 − 
                 Geitlerinema_PCC_7407_PCC_7407_GCA_000317045.1 
               
               
                   
                 4 
                 + 
                 delta_proteobacterium_HotSeep1_HS1_GCA_001577525.1 
               
               
                   
                 5 
                 + 
                 Borrelia_crocidurae_DOU_GCA_000568715.1 
               
               
                   
                 6 
                 − 
                 Streptomyces_wadayamensis_A23_GCA_000698945.1 
               
               
                   
                 7 
                 − 
                 Cyanothece_PCC_8801_uid59027 
               
               
                   
                 8 
                 − 
                 Microcoleus_PCC_7113_uid183114 
               
               
                   
                 9 
                 + 
                 Lactobacillus_fermentum_28_3_CHN_GCA_000162395.1 
               
               
                   
                 10 
                 − 
                 Cyanothece_PCC_8802_PCC_8802_GCA_000024045.1 
               
               
                   
                 11 
                 + 
                 Bacillus_mycoides_Rock3_17_GCA_000161435.1 
               
               
                   
                 12 
                 + 
                 Haloarcula_amylolytica_JCM_13557_GCA_000336615.1 
               
               
                   
                 13 
                 + 
                 Rothia_mucilaginosa_473_RMUC_GCA_001065135.1 
               
               
                   
                 14 
                 + 
                 Bacillus_thuringiensis_HD_771_uid173374 
               
               
                   
                 15 
                 + 
                 Clostridium_ljungdahlii_DSM_13528_uid50583 
               
               
                   
                 16 
                 − 
                 Clostridium_pasteurianum_BC1_uid201478 
               
               
                   
                 17 
                 + 
                 Ruminococcus_albus_7_uid51721 
               
               
                   
                 18 
                 − 
                 Synechococcus_JA_3_3Ab_JA_3_3Ab_GCA_000013205.1 
               
               
                   
                 19 
                 − 
                 Lactobacillus_equi_DPC_6820_GCA_000504525.1 
               
               
                   
                 20 
                 − 
                 Lactobacillus_agilis_Marseille_GCA_001243975.1 
               
               
                   
                 21 
                 − 
                 Cyanothece_PCC_7424_PCC_7424_GCA_000021825.1 
               
               
                   
                 22 
                 + 
                 Tolypothrix_PCC_7601_UTEX_B_481_GCA_000300115.1 
               
               
                   
                 23 
                 + 
                 Lyngbya_PCC_8106_PCC_8106_GCA_000169095.1 
               
               
                   
                 24 
                 + 
                 uncultured_archaeon_A07HR60_GCA_000496235.1 
               
               
                   
                 25 
                 + 
                 Cyanothece_PCC_8801_PCC_8801_GCA_000021805.1 
               
               
                   
                 26 
                 − 
                 Geminocystis_NIES_3709_NIES_3709_GCA_001548115.1 
               
               
                   
                 27 
                 − 
                 Leptolyngbya_NIES_3755_NIES_3755_GCA_001548435.1 
               
               
                   
                 28 
                 − 
                 Cyanothece_CCY0110_CCY0110_GCA_000169335.1 
               
               
                   
                 29 
                 − 
                 Lyngbya_PCC_8106_PCC_8106_GCA_000169095.1 
               
               
                   
                 30 
                 − 
                 Mycobacterium_tuberculosis_2228BH_GCA_000649295.1 
               
               
                   
                 31 
                 − 
                 Tolypothrix_PCC_7601_UTEX_B_481_GCA_000300115.1 
               
               
                   
                 32 
                 − 
                 Nostoc_NIES_3756_NIES_3756_GCA_001548375.1 
               
               
                   
                 33 
                 − 
                 Desmospora_8437_8437_GCA_000213595.1 
               
               
                   
                 34 
                 + 
                 Synechococcus_JA_2_3B_a_2_13_JA_2_3B_a_2_13_GCA_000013225.1 
               
               
                   
                 35 
                 − 
                 Corynebacterium_maris_DSM_45190_uid214081 
               
               
                   
                 36 
                 − 
                 Mycobacterium_smegmatis_JS623_uid184820 
               
               
                   
                 37 
                 + 
                 Mycobacterium_yongonense_05_1390_uid189649 
               
               
                   
                 38 
                 + 
                 Thermincola_ferriacetica_Z_0001_GCA_001263415.1 
               
               
                   
                 39 
                 − 
                 Clostridium_botulinum_48212_CD_GCA_001264515.1 
               
               
                   
                 40 
                 − 
                 Coprothermobacter_platensis_DSM_11748_GCA_000378005.1 
               
               
                   
                 41 
                 − 
                 Syntrophomonas_palmitatica_JCM_14374_GCA_001311885.1 
               
               
                   
                 42 
                 + 
                 Thermus_scotoductus_KI2_GCA_000744155.1 
               
               
                   
                 43 
                 + 
                 Thermincola_ferriacetica_Z_0001_GCA_001263415.1 
               
               
                   
                 44 
                 − 
                 Peptoclostridium_difficile_DA00114_GCA_000449965.2 
               
               
                   
                 45 
                 − 
                 Mycobacterium_conceptionense_MLE_GCA_001077745.1 
               
               
                   
                 46 
                 − 
                 Rothia_mucilaginosa_1211_RMUC_GCA_001060545.1 
               
               
                   
                 47 
                 − 
                 Cyanothece_PCC_7424_PCC_7424_GCA_000021825.1 
               
               
                   
                 48 
                 + 
                 Lyngbya_PCC_8106_PCC_8106_GCA_000169095.1 
               
               
                   
                 49 
                 − 
                 Streptomyces_SPB074_SPB074_GCA_000154905.1 
               
               
                   
                 50 
                 − 
                 Limnoraphis_robusta_CS_951_GCA_000972705.2 
               
               
                   
                 51 
                 + 
                 Peptoclostridium_difficile_ZJCDC_S82_GCA_000949855.1 
               
               
                   
                 52 
                 + 
                 Propionimicrobium_lymphophilum_ACS_093_V_SCH5_GCA_000411175.1 
               
               
                   
                 53 
                 + 
                 Lactobacillus_helveticus_H9_GCA_000525715.1 
               
               
                   
                 54 
                 − 
                 Scytonema_hofmanni_UTEX_2349_GCA_000582685.1 
               
               
                   
                 55 
                 + 
                 Kitasatospora_cheerisanensis_KCTC_2395_GCA_000696185.1 
               
               
                   
                 56 
                 − 
                 Spirulina_subsalsa_PCC_9445_GCA_000314005.1 
               
               
                   
                 57 
                 + 
                 Anabaena_cylindrica_PCC_7122_uid183339 
               
               
                   
                 58 
                 + 
                 Crinalium_epipsammum_PCC_9333_uid183113 
               
               
                   
                 59 
                 + 
                 Crinalium_epipsammum_PCC_9333_uid183113 
               
               
                   
                 60 
                 + 
                 Cyanothece_PCC_7425_uid59435 
               
               
                   
                 61 
                 + 
                 Cyanothece_PCC_8802_uid59143 
               
               
                   
                 62 
                 + 
                 Halothece_PCC_7418_uid183338 
               
               
                   
                 63 
                 + 
                 Microcoleus_PCC_7113_uid183114 
               
               
                   
                 64 
                 − 
                 Microcoleus_PCC_7113_uid183114 
               
               
                   
                 65 
                 + 
                 Nostoc_PCC_7120_uid57803 
               
               
                   
                 66 
                 − 
                 Dermacoccus_Ellin185_Ellin185_GCA_000152185.2 
               
               
                   
                 67 
                 + 
                 Nocardiopsis_synnemataformans_DSM_44143_GCA_000340945.1 
               
               
                   
                 68 
                 − 
                 Streptomyces_CNS606_CNS606_GCA_000426325.1 
               
               
                   
                 69 
                 + 
                 Peptoclostridium_difficile_P20_GCA_000451725.2 
               
               
                   
                 70 
                 + 
                 Chloroflexi_bacterium_JGI_0000112_G22_JGI_0000112_G22_GCA_000494585.1 
               
               
                   
                 71 
                 − 
                 Pseudomonas_URIL14HWK12_I6_URIL14HWK12_I6_GCA_000514195.1 
               
               
                   
                 72 
                 + 
                 Anoxybacillus_flavithermus_NBRC_109594_GCA_000367505.1 
               
               
                   
                 73 
                 + 
                 Cellulosilyticum_ruminicola_JCM_14822_GCA_001311925.1 
               
               
                   
                 74 
                 + 
                 Anabaena_variabilis_ATCC_29413_GCA_000204075.1 
               
               
                   
                 75 
                 − 
                 Nostoc_punctiforme_PCC_73102_GCA_000020025.1 
               
               
                   
                 76 
                 + 
                 Sulfolobus_islandicus_Y_G_57_14_GCA_000022465.1 
               
               
                   
                 77 
                 + 
                 Ammonifex_degensii_KC4_GCA_000024605.1 
               
               
                   
                 78 
                 − 
                 Meiothermus_silvanus_DSM_9946_GCA_000092125.1 
               
               
                   
                 79 
                 + 
                 Candidatus_Nitrososphaera_gargensis_Ga9_2_GCA_000303155.1 
               
               
                   
                 80 
                 − 
                 Campylobacter_fetus_venerealis_97_608_GCA_000759515.1 
               
               
                   
                 81 
                 − 
                 Methanosarcina_vacuolata_Z_761_GCA_000969905.1 
               
               
                   
                 82 
                 − 
                 Geobacillus_12AMOR1_12AMOR1_GCA_001028085.1 
               
               
                   
                 83 
                 + 
                 Clostridium_ultunense_Esp_GCA_000344075.2 
               
               
                   
                 84 
                 + 
                 Clostridium_novyi_B_NCTC_9691_GCA_000724265.2 
               
               
                   
                 85 
                 + 
                 Bacillus_cereus_MC67_GCA_000291155.1 
               
               
                   
                 86 
                 − 
                 Methylobacter_whittenburyi_UCM_B_3033_GCA_000745375.1 
               
               
                   
                 87 
                 − 
                 Streptococcus_parasanguinis_348_SPAR_GCA_001072395.1 
               
               
                   
                 88 
                 + 
                 Calothrix_PCC_7103_PCC_7103_GCA_000331305.1 
               
               
                   
                 89 
                 + 
                 Bacillus_cereus_VD140_GCA_000399545.1 
               
               
                   
                 90 
                 + 
                 Pseudonocardia_asaccharolytica_DSM_44247_NBRC_16224_GCA_000423625.1 
               
               
                   
                 91 
                 − 
                 Clostridium_perfringens_MJR7757A_GCA_001546355.1 
               
               
                   
                 92 
                 − 
                 Anoxybacillus_suryakundensis_DSM_27374_GCA_001418025.1 
               
               
                   
                   
               
            
           
         
       
     
     Example 3—Putative Type VI System 
     The signature of type VI is an effector protein with two HEPN domains ( FIG. 2 ). The HEPN domain are common in various defense systems in which the experimentally characterized ones, such as the toxins of numerous prokaryotic toxin-antitoxin systems or eukaryotic RNase L. Accordingly, once the putative type VI effector has been computationally identified, it has been predicted to function as an RNA-guided RNase. Subsequently, this prediction has been experimentally validated, and the protection by the type VI effector against the RNA bacteriophage MS2 has been demonstrated. In addition, a remarkable, novel feature of the type VI system has been discovered. Once primed with the cognate target RNA, the type VI effector (C2c2) turns into a promiscuous RNase that has a toxic, growth-inhibiting effect in bacteria. These findings demonstrate the coupling between adaptive immunity and programmed cell death (or dormancy induction) that has been previously predicted via comparative genomic analysis and mathematical modeling. 
     The new search for putative CRISPR-Cas loci (with the CRISPR seed) identified two additional large putative effectors each containing two HEPN domains and assigned to subtypes VI-B and VI-C, respectively (the C2c2-encoding loci accordingly became subtype VI-A). This classification is justified by the extremely low sequence similarity between the three groups of effectors, practically limited to the catalytic motif of the HEPN domain, the different positions of the HEPN domains with the large protein sequences, and additional features of the locus architecture in the case of subtype VI-B ( FIGS. 2 and 5 ). Specifically, the two distinct variants of subtype VI-B both encode additional proteins containing confidently predicted transmembrane domains, 4 of these in the case of VI-B1 and a single one in VI-B2 ( FIGS. 2 and 5 ). Phylogenetic analysis of the effector proteins clearly shows the split of the V-B1 and V-B2 variants in accordance with the distinct architectures of the associated (predicted) membrane proteins ( FIG. 5 ). Thus, subtype VI-B is likely to represent membrane-associated, RNA-targeting systems, a novel twist in the biology of CRISPR-Cas. Furthermore, the single-transmembrane protein of VI-B2 encompasses an additional, derived HEPN domain, the third in this system ( FIGS. 2 and 5 ). 
     Given that all (putative) type VI effectors so far discovered are similar in size to the active Class 2 effectors including subtype VI-A, it appears likely that the putative loci are functional CRISPR-Cas systems that rely on adaptation modules from other loci in the same genome. Moreover, given that RNA viruses only represent a minor component of the prokaryotic virome, it appears probable that activation of the toxin activity is the primary mechanism of action of these systems triggered by active transcription of foreign DNA. This mechanisms is likely not to be limited to type VI given the presence of HEPN domains in still poorly characterized Cas proteins present in many CRISPR-Cas systems and the experimental demonstration of the RNase activity of the Csm6 and Csx1 proteins in type III systems. 
     Example 4—Analysis of the Evolution of Class 2 CRISPR-Cas Systems 
     In extension of the previously proposed hypothesis on the independent origins of the effectors in different types and subtypes of Class 2, we harness the findings on incomplete type V loci to develop a more specific evolutionary scenario ( FIG. 7 ). As discussed above, at least 5 distinct variants within subtype V-U show evolutionary coherence and stable association with CRISPR arrays, and typically contain TnpB homologs that are intermediate in size between the compact transposon-encoded TnpB&#39;s and the large Class 2 effectors ( FIGS. 2 and 4 ), we consider these to be intermediate stages in independent paths to the emergence of new CRISPR-Cas variants. Other subtype V-U loci are not evolutionarily conserved and appear to reflect more or less random insertions of tnpB genes next to CRISPR arrays. These can be logically viewed as the earliest stages of evolution of CRISPR-Cas systems. Notably, all subtype V-U loci lack the adaptation modules suggesting that the first stage of evolution of new Class 2 CRISPR-Cas involves insertion of a TnpB-encoding element next to an orphan CRISPR array ( FIG. 7 ). At the next step, the association between CRISPR and a TnpB derivative becomes fixed in the microbial population, conceivably due to the emergence of function the exact nature of which remains to be understood and accompanied by an increase in the size of the protein via internal duplications and/or insertion of additional domains ( FIG. 7 ). The final steps include further growth of the effector protein resulting in the typical bilobed structure and, at least in some cases, association with an adaptation module through recombination with a different CRISPR-cas locus ( FIG. 7 ). 
     A similar scenario could apply to the type VI systems ( FIG. 7 ). In this case, the first step would involve insertion of a toxin-antitoxin module next to a CRISPR array, followed by a duplication of the HEPN-containing toxin gene accompanied by attenuation or masking of the toxicity and the loss of the antitoxin gene. Alternatively or additionally, and evolutionary connection between the type VI effectors and HEPN domain-containing proteins in other CRISPR-Cas variants cannot be ruled out. The subsequent evolution would include further expansion of the double-HEPN protein to the typical size of a Class 2 effector and acquisition of an adaptation module ( FIG. 7 ). 
     Example 5—Amended Classification of Class 2 CRISPR-Cas Systems 
     The systematic search for novel Class 2 CRISPR-Cas loci described here has led to a major expansion of the known diversity of these systems. Instead of the two types and 4 subtypes included in the latest classification, there are now three types and at least 10 subtypes ( FIG. 2 ). Despite the lack of functional data on subtype V-U, it appears likely that some variants in this provisional subtype, particularly V-U3, are eventually upgraded to the subtype status. Given the comprehensive character of the search described here (see  FIG. 1 ), there may not be many new variants are discovered except for rare ones or possibly those that are restricted in their spread to particular groups of prokaryotes that are not adequately represented in current sequence databases. It should be noted, however, that the current subtype V-U is a heterogeneous assemblage of diverse loci that we provisionally kept together given the likely possibility that these are not typical, active CRISPR-Cas systems. Functional characterization of these variants will provide for a more granular classification. 
     Example 6—Functional Diversity of Class 2 CRISPR-Cas Systems 
     Although functional characterization of the Class 2 subtypes is not complete, even at this stage, remarkable functional diversity is apparent. The manifestations of this diversity include different target (dsDNA for types II and V, but RNA for type VI); the requirement for tracrRNA (type II and subtype V-B but not subtype V-A or type VI), the sequence of the protospacer-adjacent motif (PAM), and character of the cut introduced into the target nucleic acid (Table 2). This functional diversity is a major incentive for further characterization of different Class 2 systems as it creates opportunities for the development of various, specialized genome editing and engineering tools. In particular, effectors that do not depend on tracrRNA are attractive for their simplicity. The potential for the creation of new, conceivably, improved tools has already been demonstrated with the type V-A effector (Cpf1). Type VI systems could add a whole new dimension allowing for multiple RNA-targeting tools and possibly harnessing the programmed cell death-inducing capacity to kill cells expressing specific transcripts. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Functional diversity of the Class 2 CRISPR-Cas systems 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Nuclease 
                   
                   
                   
                   
               
               
                   
                 domains 
                 tracrRNA 
                 PAM 
                 Substrate 
                 Target cut 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Type II: 
                 TnpB/ 
                 Yes 
                 3′, 
                 dsDNA 
                 Blunt ends 
               
               
                 Cas9 
                 RuvC + 
                   
                 GC-rich 
               
               
                   
                 HNH 
               
               
                 Type V-A: 
                 TnpB/ 
                 No 
                 5′, 
                 dsDNA 
                 Staggered 
               
               
                 Cas12a/Cpf1 
                 RuvC + 
                   
                 AT-rich 
                   
                 ends, 5′ 
               
               
                   
                 Nuc 
                   
                   
                   
                 overhangs 
               
               
                 Type V-B: 
                 TnpB/ 
                 Yes 
                 5′, 
                 dsDNA 
                 ? 
               
               
                 Cas12b/C2c1 
                 RuvC + ? 
                   
                 AT-rich 
               
               
                 Type VI-A: 
                 2xHEPN 
                 No 
                 5′, 
                 ssRNA 
                 Unspecific 
               
               
                 Cas13a/C2c2 
                   
                   
                 GC-rich 
                   
                 RNA cuts + 
               
               
                   
                   
                   
                   
                   
                 collateral 
               
               
                   
                   
                   
                   
                   
                 RNA 
               
               
                   
                   
                   
                   
                   
                 cleavage 
               
               
                   
               
            
           
         
       
     
     Example 7—Comprehensive Census of Class 2 CRISPR-Cas Loci in Bacterial and Archaeal Genomes 
     The procedure that was employed here for the detection of the types and subtypes of Class 2 loci (see  FIG. 1 ) can be expected to identify (nearly) all variants of such systems present in the currently available bacterial and archaeal genomes. Indeed, under the assumption that a functional Class2 effector has to be a large protein, we examined all such proteins encoded in the vicinity of CRISPR arrays and/or cas1 genes. We therefore were interested in a comprehensive census of Class 2 types and subtypes in the current set of complete bacterial and archaeal genomes. To this end, we constructed sequence profiles for the effectors of all identified Class 2 subtypes and compared these to the proteins encoded in the 5000 available complete prokaryotic genomes. This procedure ensured comprehensive detection of all instances of each effector including highly diverged variants. The neighborhoods of the respective genes were then examined for the presence of CRISPR arrays and additional cas genes as previously described. 
     The most striking observation is the dramatic dominance of type II which is represented in about 10% of bacterial genomes (Table 3). Both type V and type VI are more than an order of magnitude less abundant, in agreement with the expectation that the CRISPR-Cas types and subtypes remaining to be discovered are rare variants. An intriguing question is whether type II is in some fashion “more fit”, i.e. more efficient in defense or incurs a lower cost, than other Class 2 variants. Most of the Class 2 subtypes are represented in taxonomically diverse bacteria which is indicative of horizontal gene transfer as the dominant process in CRISPR-Cas evolution. It is notable, however, that the relatively abundant subtype VI-B, the only CRISPR-Cas system that is predicted to be membrane-associated, appears to be restricted to the phylum  Bacteroidetes,  perhaps reflecting some unique aspect of the biology of these bacteria. Similarly, the V-U5 variant that encompasses an inactivated TnpB homolog is limited to Cyanobacteria, being perhaps involved in a unique regulatory pathway. A major puzzle that has been emphasized previously and becomes all the more striking with the present expansion of the diversity of Class 2 systems is that, apart from two instances of subtype V-A identified in mesophilic archaea, Class 2 systems are unique to bacteria. This exclusion of Class 2 systems from archaea implies a major functional distinction between the two classes of CRISPR-Cas systems the nature of which remains enigmatic 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 A comprehensive census of Class 2 CRISPR-Cas systems in bacterial and archaeal genomes 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 (Sub)type 
                 II 
                 V-A 
                 V-B 
                 V-U 
                 VI-A 
                 VI-B 
                 VI-C 
               
               
                   
               
               
                 Effector 
                 Cas9 
                 Cas12a 
                 Cas12b 
                 C2c4, C2c5; 
                 Cas13a 
                 Cas13b 
                 Cas13c 
               
               
                   
                   
                 (cpf1) 
                 (C2c1) 
                 5 distinct 
                 (C2c2) 
                 (C2c6) 
                 (C2c7) 
               
               
                   
                   
                   
                   
                 subgroups 
               
               
                   
                   
                   
                   
                 (V-U1-5) 
               
               
                 Number 
                 3822 
                 70 
                 18 
                 92 
                 30 
                 94 
                 6 
               
               
                 of loci 
                 2109 II-A 
               
               
                   
                 130 II-B 
               
               
                   
                 1573 II-C 
               
               
                   
                 10 
               
               
                   
                 unassigned 
               
               
                 Representation 
                 Diverse 
                 Diverse 
                 Diverse 
                 Diverse 
                 Diverse 
                 Bacteroidetes 
                 Fusobacteria/ 
               
               
                   
                 bacteria 
                 bacteria + 
                 bacteria 
                 bacteria 
                 bacteria 
                   
                 Clostridia 
               
               
                   
                   
                 2 archaea 
               
               
                 Other cas 
                 85% 
                 70% 
                 65% 
                 NONE 
                 25% 
                 NONE 
                 NONE 
               
               
                 genes 
                 cas1 + cas2; 
                 cas1 + cas 
                 cas1 + 
                   
                 cas1 + 
               
               
                   
                 55% csn2; 
                 255% 
                 cas2 + 
                   
                 cas2 
               
               
                   
                 3% cas4 
                 cas4 
                 cas4 
               
               
                 % loci 
                 65% 
                 68% 
                 60% 
                 ~50% 
                 73% 
                 90% 
                 83% 
               
               
                 containing 
               
               
                 CRISPR 
               
               
                 array 
               
               
                   
               
            
           
         
       
     
     The genomic analysis presented here substantially expands the diversity of Class 2 CRISPR-Cas systems. In particular, these new variants show unprecedented functional features, such as independence of a tracrRNA in subtype V-A as well as exclusive RNA targeting coupled with the induction of the toxic effect in subtype VI-A and likely in all type VI systems. The subtype V-U can be expected to show even more unusual properties. This functional diversity provides the potential for the development of new, versatile genome editing and regulation tools. We provide compelling evidence of independent origin of different Class 2 types and subtypes from mobile elements. The discovered remarkable diversity notwithstanding, it should be noted that the procedure applied here provides for a (near) exhaustive identification of Class 2 systems. Whatever additional variants remain to be found, they are likely either rare or confined to groups of bacteria that are currently unknown or poorly sampled. 
     In the foregoing description, it will be readily apparent to one skilled in the art that varying substitutions and modifications may be made to the invention disclosed herein without departing from the scope and spirit of the invention. The invention illustratively described herein suitably may be practiced in the absence of any element or elements, limitation or limitations, which is not specifically disclosed herein. The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention that in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention. Thus, it should be understood that although the present invention has been illustrated by specific embodiments and optional features, modification and/or variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scopes of this invention.