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Definitions

• RNA-guided Fokl Nucleases RNNs
• RNA-guided genome editing e.g., editing using CRISPR/Cas9 systems
• FNNs RNA-guided Fokl Nucleases
• FokI-dCas9 fusion proteins e.g., FokI-dCas9 fusion proteins
• CRISPR clustered, regularly interspaced, short palindromic repeats
• Cas CRISPR-associated systems
• the Cas9 nuclease from S. pyogenes can be guided via base pair complementarity between the first 20 nucleotides of an engineered gRNA and the complementary strand of a target genomic DNA sequence of interest that lies next to a protospacer adjacent motif (PAM), e.g., a PAM matching the sequence NGG or NAG (Shen et al, Cell Res (2013); Dicarlo et al, Nucleic Acids Res (2013); Jiang et al, Nat Biotechnol 31 , 233-239 (2013); Jinek et al, Elife 2, e00471 (2013); Hwang et al, Nat Biotechnol 31, 227-229 (2013); Cong et al, Science 339, 819-823 (2013); Mali et al, Science 339, 823-826 (2013c); Cho et al, Nat
• CRISPR-Cas nucleases can tolerate up to five mismatches and still cleave; it is hard to predict the effects of any given single or combination of mismatches on activity. Taken together, these nucleases can show significant off-target effects but it can be challenging to predict these sites. Described herein are methods for increasing the specificity of genome editing using the
• RNA-guided Fokl Nucleases e.g., Fokl- Cas9 or FokI-dCas9-based fusion proteins.
• the invention provides FokI-dCas9 fusion proteins, comprising a Fokl catalytic domain sequence fused to the terminus, e.g., the N terminus, of dCas9, optionally with an intervening linker, e.g., a linker of from 2-30 amino acids, e.g., 4-12 amino acids, e.g., Gly 4 Ser.
• the Fokl catalytic domain comprises amino acids 388-583 or 408-583 of SEQ ID NO:4.
• the dCas9 comprises mutations at the dCas9 comprises mutations at D10, E762, H983, or D986; and at H840 or N863; e.g., at: (i) DIOA or DION; and (ii) H840A, H840Y or H840N.
• the invention provides nucleic acids encoding these fusion proteins, vector comprising the nucleic acids, and host cells harboring or expressing the nucleic acids, vectors, or fusion proteins.
• the invention provides methods for inducing a sequence- specific break in a double-stranded DNA molecule, e.g., in a genomic sequence in a cell, the method comprising expressing in the cell, or contacting the cell with, the FokI-dCas9 fusion protein described herein, and:
• each of the two single guide R As include sequences that are each complementary to one strand of the target sequence such that using both guide RNAs results in targeting both strands (i.e., one single guide RNA targets a first strand, and the other guide RNA targets the complementary strand), and Fokl cuts each strand resulting in a pair of nicks on opposite DNA strands, thereby creating a double-stranded break, or
• each of the two crRNAs include sequences that are complementary to one strand of the target sequence such that using both crRNAs results in targeting both strands (i.e., one crRNA targets a first strand, and the other crRNA targets the complementary strand), and Fokl cuts each strand resulting in a pair of nicks on opposite DNA strands, thereby creating a double- stranded break.
• the invention provides methods for increasing specificity of RNA-guided genome editing in a cell, the method comprising contacting the cell with an RNA-guided Fokl Nuclease (RFN) fusion protein described herein.
• RFN RNA-guided Fokl Nuclease
• the method may further comprise expressing in the cell, or contacting the cell with, (a) two single guide RNAs, wherein each of the two single guide RNAs include sequences that are each complementary to one strand of the target sequence such that using both guide RNAs results in targeting both strands (i.e., one single guide RNA targets a first strand, and the other guide RNA targets the complementary strand), and Fokl cuts each strand resulting in a pair of nicks on opposite DNA strands, thereby creating a double-stranded break, or
• each of the two crRNAs include sequences that are complementary to one strand of the target sequence such that using both crRNAs results in targeting both strands (i.e., one crRNA targets a first strand, and the other crRNA targets the complementary strand), and Fokl cuts each strand resulting in a pair of nicks on opposite DNA strands, thereby creating a double- stranded break.
• the two target genomic sequences i.e., the sequences to which the target complementarity regions of the crR A or single guide R As are complementary
• an indel mutation is induced between the two target sequences.
• the specificity of RNA-guided genome editing in a cell is increased.
• Figure 1 Schematic illustrating a gR A/Cas9 nuclease complex bound to its target DNA site. Scissors indicate approximate cleavage points of the Cas9 nuclease on the genomic DNA target site. Note the numbering of nucleotides on the guide RNA proceeds in an inverse fashion from 5' to 3'.
• FIG. 2B Schematic overview of the EGFP disruption assay. Repair of targeted Cas9-mediated double-stranded breaks in a single integrated EGFP-PEST reporter gene by error-prone NHEJ-mediated repair leads to frame-shift mutations that disrupt the coding sequence and associated loss of fluorescence in cells.
• Figures 2C-F Activities of RGNs harboring sgRNAs bearing (C) single mismatches, (D) adjacent double mismatches, (E) variably spaced double mismatches, and (F) increasing numbers of adjacent mismatches assayed on three different target sites in the EGFP reporter gene sequence. Mean activities of replicates (see Online Methods) are shown, normalized to the activity of a perfectly matched gRNA. Error bars indicate standard errors of the mean. Positions mismatched in each gRNA are highlighted in grey in the grid below. Sequences of the three EGFP target sites were as follows:
• EGFP Site 1 GGGCACGGGCAGCTTGCCGGTGG (SEQ ID NO : 1 )
• EGFP Site 2 GATGCCGTTCTTCTGCTTGTCGG (SEQ ID NO:2)
• EGFP Site 3 GGTGGTGCAGATGAACTTCAGGG (SEQ ID NO:3)
• Figure 2G Mismatches at the 5' end of the gRNA make CRISPR/Cas more sensitive more 3' mismatches.
• the gRNAs Watson-Crick base pair between the RNA&DNA with the exception of positions indicated with an "m" which are mismatched using the Watson-Crick transversion (i.e. EGFP Site#2 M18-19 is mismatched by changing the gRNA to its Watson-Crick partner at positions 18 & 19.
• positions near the 5 ' of the gRNA are generally very well tolerated, matches in these positions are important for nuclease activity when other residues are mismatched.
• Figure 2H Efficiency of Cas9 nuclease activities directed by gRNAs bearing variable length complementarity regions ranging from 15 to 25 nts in a human cell- based U20S EGFP disruption assay. Expression of a gRNA from the U6 promoter requires the presence of a 5 ' G and therefore it was only possible to evaluate gRNAs harboring certain lengths of complementarity to the target DNA site (15, 17, 19, 20, 21, 23, and 25 nts).
• Figure 3B Efficiencies of targeted indel mutations introduced at seven different human endogenous gene targets by matched standard and tru-RGNs.
• Figure 3C DNA sequences of indel mutations induced by RGNs using a tru- gRNA or a matched full-length gRNA targeted to the EMXl site.
• the portion of the target DNA site that interacts with the gRNA complementarity region is highlighted in grey with the first base of the PAM sequence shown in lowercase. Deletions are indicated by dashes highlighted in grey and insertions by italicized letters highlighted in grey. The net number of bases deleted or inserted and the number of times each sequence was isolated are shown to the right.
• FIG. 3E U20S.EGFP cells were transfected with variable amounts of full- length gRNA expression plasmids (top) or tru-gRNA expression plasmids (bottom) together with a fixed amount of Cas9 expression plasmid and then assayed for percentage of cells with decreased EGFP expression. Mean values from duplicate experiments are shown with standard errors of the mean. Note that the data obtained with tru-gRNA matches closely with data from experiments performed with full- length gRNA expression plasmids instead of tru-gRNA plasmids for these three EGFP target sites.
• Figure 3F U20S.EGFP cells were transfected with variable amount of Cas9 expression plasmid together with variable amounts of full-length gRNA expression plasmids (top) or tru-gRNA expression plasmids (bottom) (amounts determined for each tru-gRNA from the experiments of Figure 3E). Mean values from duplicate experiments are shown with standard errors of the mean. Note that the data obtained with tru-gRNA matches closely with data from experiments performed with full- length gRNA expression plasmids instead of tru-gRNA plasmids for these three EGFP target sites. The results of these titrations determined the concentrations of plasmids used in the EGFP disruption assays performed in Examples 1 and 2.
• Figures 4A-C RNA-guided Fokl nucleases and a CRISPR/Cas Subtype Ypest protein 4 (Csy4)-based multiplex gRNA expression system.
• FIG. 1 Schematic overview of a Csy4-based multiplex gRNA expression system.
• Two gRNAs (with any 5 ' end nucleotide) are co-expressed in a single transcript from a U6 promoter with each gRNA flanked by Csy4 recognition sites.
• Csy4 cleaves and releases gRNAs from the transcript.
• the Csy4 recognition site remains at the 3 ' end of the gRNA with a Csy4 nuclease bound to that site.
• Figures 5A-F Design and optimization of RNA-guided Fokl nucleases.
• FIGS 6A-D Dimerization of FokI-dCas9 RFNs is required for efficient genome editing activity.
• MLHl mutL homo log 1
• FIGS 7A-B Mutagenic activities of a Cas9 nickase or FokI-dCas9 co- expressed with a single gRNA.
• Indel mutation frequencies were determined by deep sequencing. Each indel frequency value reported was determined from a single deep sequencing library prepared from genomic DNA pooled from three independent transfection
• VEGFA Vascular Endothelial Growth Factor A
• DDB2 Damage- Specific DNA Binding Protein 2
• FANCF Fanconi Anemia, Complementation Group F
• FES Feline Sarcoma Oncogene
• RUNX Runt-Related Transcription Factor 1.
• Figures 8A-C Single Cas9 nickases can introduce point mutations with high efficiencies into their target sites.
• RGNs CRISPR RNA-guided nucleases
• T7EI assay (which, as performed in our laboratory, has a reliable detection limit of ⁇ 2 to 5% mutation frequency). Because these mutation rates were very high, it was possible to avoid using deep sequencing methods previously required to detect much lower frequency ZFN- and TALEN-induced off-target alterations (Pattanayak et al., Nat Methods 8, 765-770 (2011); Perez et al, Nat Biotechnol 26, 808-816 (2008);
• off-target sites were seen for a number of RGNs, identification of these sites was neither comprehensive nor genome -wide in scale. For the six RGNs studied, only a very small subset of the much larger total number of potential off-target sequences in the human genome was examined. Although examining such large numbers of loci for off-target mutations by T7EI assay is neither a practical nor a cost-effective strategy, the use of high-throughput sequencing in future studies might enable the interrogation of larger numbers of candidate off-target sites and provide a more sensitive method for detecting bona fide off-target mutations. For example, such an approach might enable the unveiling of additional off-target sites for the two RGNs for which we failed to uncover any off-target mutations.
• a number of strategies can be used to minimize the frequencies of genomic off-target mutations.
• the specific choice of RGN target site can be optimized; given that off-target sites that differ at up to five positions from the intended target site can be efficiently mutated by RGNs, choosing target sites with minimal numbers of off-target sites as judged by mismatch counting seems unlikely to be effective; thousands of potential off-target sites that differ by four or five positions within the 20 bp RNA:DNA complementarity region will typically exist for any given RGN targeted to a sequence in the human genome. It is also possible that the nucleotide content of the gRNA complementarity region might influence the range of potential off-target effects.
• RNA:DNA hybrids For example, high GC-content has been shown to stabilize RNA:DNA hybrids (Sugimoto et al, Biochemistry 34, 1121 1-11216 (1995)) and therefore might also be expected to make gRNA/genomic DNA hybridization more stable and more tolerant to mismatches. Additional experiments with larger numbers of gRNAs will be needed to assess if and how these two parameters (numbers of mismatched sites in the genome and stability of the RNA:DNA hybrid) influence the genome-wide specificities of RGNs. However, it is important to note that even if such predictive parameters can be defined, the effect of implementing such guidelines would be to further restrict the targeting range of RGNs.
• RGN-induced off-target effects might be to reduce the concentrations of gRNA and Cas9 nuclease expressed in the cell. This idea was tested using the RGNs for VEGFA target sites 2 and 3 in
• CRISPR-Cas RNA-guided nucleases based on the S.
• pyogenes Cas9 protein can have significant off-target mutagenic effects that are comparable to or higher than the intended on-target activity (Example 1). Such off-target effects can be problematic for research and in particular for potential therapeutic applications. Therefore, methods for improving the specificity of
• RGNs RNA guided nucleases
• Cas9 RGNs can induce high-frequency indel mutations at off-target sites in human cells (see also Cradick et al., 2013; Fu et al., 2013; Hsu et al., 2013; Pattanayak et al, 2013). These undesired alterations can occur at genomic sequences that differ by as many as five mismatches from the intended on- target site (see Example 1).
• RNA-guided nucleases are to be used for research and therapeutic applications.
• Dimerization is an attractive potential strategy for improving the specificity of Cas9 nucleases. This is distinct from a paired Cas9 nickase approach, which is not a true dimeric system. Paired nickases work by co-localizing two Cas9 nickases on a segment of DNA, thereby inducing high efficiency genome editing via an undefined mechanism. Because dimerization is not required for enzymatic activity, single Cas9 nickases can also induce indels with high efficiencies at certain sites (via an unknown mechanism) and can therefore potentially cause unwanted off-target mutations in the genome.
• one strategy to improve the specificity of RGNs is fusing a Fokl endonuclease domain to a catalytically inactive form of Cas9 bearing the D10A and H840A mutations (also known as dCas9).
• Fokl nuclease domain functions as a dimer and therefore two subunits must be recruited to the same local piece of DNA in order to induce a double-stranded break.
• Figure 9A and Example 2 two FokI-dCas9 fusions are recruited in an appropriate configuration using two different gRNAs to yield a double-stranded break.
• the Fokl- dCas9 fusions would bind to a site that is twice as long as that of a single RGN and therefore this system would be expected to be more specific.
• FokI-dCas9 fusion proteins wherein the Fokl sequence is fused to dCas9 (preferably to the amino-terminal end of dCas9, but also optionally to the carboxy terminus), optionally with an intervening linker, e.g., a linker of from 2-30 amino acids, e.g., 4-12 amino acids, e.g., Gly 4 Ser (SEQ ID NO:23) or (Gly 4 Ser) 3 .
• the fusion proteins include a linker between the dCas9 and the Fokl domains.
• Linkers that can be used in these fusion proteins (or between fusion proteins in a concatenated structure) can include any sequence that does not interfere with the function of the fusion proteins.
• the linkers are short, e.g., 2-20 amino acids, and are typically flexible (i.e., comprising amino acids with a high degree of freedom such as glycine, alanine, and serine).
• the linker comprises one or more units consisting of GGGS (SEQ ID NO:22) or GGGGS (SEQ ID NO:23), e.g., two, three, four, or more repeats of the GGGS (SEQ ID NO:22) or GGGGS (SEQ ID NO:23) unit.
• linker sequences can also be used.
• a RNA-guided Fokl nuclease platform in which dimerization, rather than just co-localization, is required for efficient genome editing activity. These nucleases can robustly mediate highly efficient genome editing in human cells and can reduce off-target mutations to undetectable levels as judged by sensitive deep sequencing methods. Also described is an efficient system for expressing pairs of gRNAs with any 5 ' end nucleotide, a method that confers a wider targeting range on the RFN platform. Finally, monomeric Cas9 nickases generally introduce more undesirable indels and point mutations than the nucleases described herein in the presence of a single gRNA.
• RNA-guided Fokl Nuclease (RFN) platform for performing robust and highly specific genome editing in human cells.
• RFNs require two gRNAs for activity and function as dimers.
• the engineering of an active RFN required fusion of the Fokl nuclease domain to the amino-terminal end of the dCas9 protein, an architecture different from ZFNs and TALENs in which the Fokl domain is fused to the carboxy-terminal end of engineered zinc finger or transcription activator-like effector repeat arrays.
• RFNs also require that the half-sites bound by each Fok-dCas9/gRNA complex have a particular relative orientation (PAMs out) with a relatively restricted intervening spacer length of 14 to 17 bps (although activity may be possible at additional spacings but with less consistent success).
• PAMs out relative orientation
• RFNs The dimeric nature of RFNs provides important specificity advantages relative to standard monomeric Cas9 nucleases. In an ideal dimeric system, little to no activity will be observed with monomers on half-sites.
• the present data demonstrate that FokI-dCas9 directed by a single gRNA induces very little or no mutagenesis at RFN half-sites. 12 single gRNAs (for six RFN target sites) were tested with co- expressed FokI-dCas9 and indels were observed at very low frequencies (range of 0.0045% to 0.47%), in some cases at levels as low as background rates observed in control cells in which there was no expression of gRNA or nuclease.
• Fokl nuclease domain functions as a dimer
• any indels observed with a single gR A are likely due to recruitment of a FokI-dCas9 dimer to the DNA.
• FokI-dCas9 dimer Regardless of mechanism, given that only very low level mutagenesis was observed when FokI-dCas9 was tested with single gRNAs at 12 on-target half-sites, it is very unlikely that any mutagenesis will be induced at partially mismatched, off-target half- sites. Indeed, an RFN targeted to VEGFA did not induce detectable mutations at known off-target sites of one of the gRNAs as judged by deep sequencing.
• RFNs are a true dimeric system, they possess a number of important advantages over paired nickase technology, which depends on co-localization but does not require dimerization.
• paired Cas9 nickases show greater promiscuity in the orientation and spacing of target half-sites than dimeric RFNs and therefore have a greater potential range of sites at which off-target mutations might be induced.
• Paired nickase half-sites can be oriented with their PAMs in or PAMs out and with spacer sequences ranging in length from 0 to 1000 bps (Ran et al, Cell 154, 1380-1389 (2013); Mali et al, Nat Biotechnol 31, 833-838 (2013); Cho et al, Genome Res (2013)).
• This promiscuity exists because the genome editing activities of Cas9 nickases do not depend on dimerization of the enzyme but rather just co- localization of the two nicks.
• RFNs are much more stringent in their specificities— half-sites must have their PAMs out and must be spaced apart by 14 to 17 bps, due to the requirement for two appropriately positioned Fokl cleavage domains for efficient cleavage.
• Fokl is a type lis restriction endonuclease that includes a DNA recognition domain and a catalytic (endonuclease) domain.
• the fusion proteins described herein can include all of Fokl or just the catalytic endonuclease domain, e.g., amino acids 388-583 or 408-583 of GenBank Acc. No. AAA24927.1, e.g., as described in Li et al, Nucleic Acids Res. 39(1): 359-372 (2011); Cathomen and Joung, Mol. Ther. 16: 1200-1207 (2008), or a mutated form of Fokl as described in Miller et al. Nat
• An exemplary nucleic acid sequence encoding Fokl is as follows:
• the Fokl nuclease used herein is at least about 50% identical SEQ ID NO:4, e.g., to amino acids 388-583 or 408-583 of SEQ ID NO:4. These variant nucleases must retain the ability to cleave DNA.
• the nucleotide sequences are about 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99% or 100% identical to amino acids 388-583 or 408-583 of SEQ ID NO:4. In some embodiments, any differences from amino acids 388-583 or 408-583 of SEQ ID NO:4 are in non-conserved regions.
• the sequences are aligned for optimal comparison purposes (gaps are introduced in one or both of a first and a second amino acid or nucleic acid sequence as required for optimal alignment, and non-homologous sequences can be disregarded for comparison purposes).
• the length of a reference sequence aligned for comparison purposes is at least 50%> (in some embodiments, about 50%, 55%, 60%, 65%, 70%, 75%, 85%, 90%, 95%, or 100% of the length of the reference sequence is aligned).
• the nucleotides or residues at corresponding positions are then compared. When a position in the first sequence is occupied by the same nucleotide or residue as the corresponding position in the second sequence, then the molecules are identical at that position.
• the percent identity between the two sequences is a function of the number of identical positions shared by the sequences, taking into account the number of gaps, and the length of each gap, which need to be introduced for optimal alignment of the two sequences.
• the comparison of sequences and determination of percent identity between two sequences can be accomplished using a mathematical algorithm.
• the percent identity between two amino acid sequences is determined using the Needleman and Wunsch ((1970) J. Mol. Biol. 48:444-453) algorithm which has been incorporated into the GAP program in the GCG software package, using a Blossum 62 scoring matrix with a gap penalty of 12, a gap extend penalty of 4, and a frameshift gap penalty of 5.
• a number of bacteria express Cas9 protein variants.
• Streptococcus pyogenes is presently the most commonly used; some of the other Cas9 proteins have high levels of sequence identity with the S. pyogenes Cas9 and use the same guide R As. Others are more diverse, use different gR As, and recognize different PAM sequences as well (the 2-5 nucleotide sequence specified by the protein which is adjacent to the sequence specified by the RNA). Chylinski et al. classified Cas9 proteins from a large group of bacteria (RNA Biology 10:5, 1-12; 2013), and a large number of Cas9 proteins are listed in supplementary figure 1 and supplementary table 1 thereof, which are incorporated by reference herein. Additional Cas9 proteins are described in Esvelt et al., Nat Methods.
• Cas9 molecules of a variety of species can be used in the methods and compositions described herein. While the S. pyogenes and S. thermophilus Cas9 molecules are the subject of much of the disclosure herein, Cas9 molecules of, derived from, or based on the Cas9 proteins of other species listed herein can be used as well. In other words, while the much of the description herein uses S. pyogenes and S. thermophilus Cas9 molecules, Cas9 molecules from the other species can replace them. Such species include those set forth in the following table, which was created based on supplementary figure 1 of Chylinski et al, 2013.
• the constructs and methods described herein can include the use of any of those Cas9 proteins, and their corresponding guide RNAs or other guide RNAs that are compatible.
• the Cas9 from Streptococcus thermophilus LMD-9 CRISPR1 system has also been shown to function in human cells in Cong et al (Science 339, 819 (2013)).
• Cas9 orthologs from N. meningitides are described in Hou et al, Proc Natl Acad Sci U S A. 2013 Sep 24;110(39): 15644-9 and Esvelt et al, Nat Methods. 2013 Nov;10(l 1): 1116-21. Additionally, Jinek et al. showed in vitro that Cas9 orthologs from S. thermophilus and L.
• innocua (but not from N. meningitidis or C. jejuni, which likely use a different guide RNA), can be guided by a dual S. pyogenes gRNA to cleave target plasmid DNA, albeit with slightly decreased efficiency.
• the present system utilizes the Cas9 protein from S. pyogenes, either as encoded in bacteria or codon-optimized for expression in mammalian cells, containing mutations at D10, E762, H983, or D986 and H840 or N863, e.g., D10A/D10N and H840A/H840N/H840Y, to render the nuclease portion of the protein catalytically inactive; substitutions at these positions could be alanine (as they are in Nishimasu al, Cell 156, 935-949 (2014)) or they could be other residues, e.g., glutamine, asparagine, tyrosine, serine, or aspartate, e.g.,, E762Q, H983N, H983Y, D986N, N863D, N863S, or N863H ( Figure 1C).
• S. pyogenes either as encoded in bacteria or codon-optimized for expression in
• sequence of the catalytically inactive S. pyogenes Cas9 that can be used in the methods and compositions described herein is as follows; the exemplary mutations of D10A and H840A are in bold and underlined. 10 20 30 40 50 60
• PAAFKYFDTT IDRKRYTSTK EVLDATLIHQ SITGLYETRI DLSQLGGD SEQ ID NO: 5
• the Cas9 nuclease used herein is at least about 50% identical to the sequence of S. pyogenes Cas9, i.e., at least 50% identical to SEQ ID NO:5.
• the nucleotide sequences are about 50%>, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99% or 100% identical to SEQ ID NO:5.
• any differences from SEQ ID NO:5 are in non-conserved regions, as identified by sequence alignment of sequences set forth in Chylinski et al, RNA Biology 10:5, 1-12; 2013 (e.g., in supplementary figure 1 and supplementary table 1 thereof); Esvelt et al, Nat Methods. 2013 Nov; 10(11): 1116-21 and Fonfara et al, Nucl. Acids Res. (2014) 42 (4): 2577-2590. [Epub ahead of print 2013 Nov 22] doi: 10.1093/nar/gktl074. Identity is determined as set forth above.
• gRNAs Guide RNAs
• RNAs generally speaking come in two different systems: System 1, which uses separate crRNA and tracrRNAs that function together to guide cleavage by Cas9, and System 2, which uses a chimeric crRNA-tracrRNA hybrid that combines the two separate guide RNAs in a single system (referred to as a single guide RNA or sgRNA, see also Jinek et al., Science 2012; 337:816-821).
• the tracrRNA can be variably truncated and a range of lengths has been shown to function in both the separate system (system 1) and the chimeric gRNA system (system 2).
• tracrRNA may be truncated from its 3' end by at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35 or 40 nts.
• the tracrRNA molecule may be truncated from its 5' end by at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35 or 40 nts.
• the tracrRNA molecule may be truncated from both the 5' and 3' end, e.g., by at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15 or 20 nts on the 5' end and at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35 or 40 nts on the 3' end.
• vectors e.g., plasmids
• plasmids encoding more than one gRNA are used, e.g., plasmids encoding, 2, 3, 4, 5, or more gRNAs directed to different sites in the same region of the target gene.
• Cas9 nuclease can be guided to specific 17-20 nt genomic targets bearing an additional proximal protospacer adjacent motif (PAM), e.g., of sequence NGG, using a guide RNA, e.g., a single gRNA or a tracrRNA/crRNA, bearing 17-20 nts at its 5' end that are complementary to the complementary strand of the genomic DNA target site.
• PAM proximal protospacer adjacent motif
• the present methods can include the use of a single guide RNA comprising a crRNA fused to a normally trans-encoded tracrRNA, e.g., a single Cas9 guide RNA as described in Mali et al, Science 2013 Feb 15; 339(6121):823-6, with a sequence at the 5' end that is complementary to the target sequence, e.g., of 25-17, optionally 20 or fewer nucleotides (nts), e.g., 20, 19, 18, or 17 nts, preferably 17 or 18 nts, of the complementary strand to a target sequence immediately 5 Of a protospacer adjacent motif (PAM), e.g., NGG, NAG, or NNGG
• the single Cas9 guide RNA consists of the sequence:
• X17-20 is the nucleotide sequence complementary to 17-20 consecutive nucleotides of the target sequence.
• DNAs encoding the single guide RNAs have been described previously in the literature (Jinek et al, Science. 337(6096):816-21 (2012) and Jinek et al, Elife. 2:e00471 (2013)).
• the guide RNAs can include X N which can be any sequence, wherein N (in the RNA) can be 0-200, e.g., 0-100, 0-50, or 0-20, that does not interfere with the binding of the ribonucleic acid to Cas9.
• the guide RNA includes one or more Adenine (A) or Uracil (U) nucleotides on the 3 ' end.
• the RNA includes one or more U, e.g., 1 to 8 or more Us (e.g., U, UU, UUU, UUUU, UUUUU, UUUUU, UUUUUU, UUUUUU, UUUUUU, UUUUUUUUUU, UUUUUUUUUUU) at the 3' end of the molecule, as a result of the optional presence of one or more Ts used as a termination signal to terminate RNA PolIII transcription.
• gRNA e.g., the crRNA and tracrRNA found in naturally occurring systems.
• a single tracrRNA would be used in conjunction with multiple different crRNAs expressed using the present system, e.g., the following:
• the methods include contacting the cell with a tracrRNA comprising or consisting of the sequence
• the tracrRNA molecule may be truncated from its 3' end by at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35 or 40 nts.
• the tracrR A molecule may be truncated from its 5 ' end by at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35 or 40 nts.
• the tracrRNA molecule may be truncated from both the 5' and 3' end, e.g., by at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15 or 20 nts on the 5' end and at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35 or 40 nts on the 3' end.
• Exemplary tracrRNA sequences in addition to SEQ ID NO: 8 include the following:
• GGCACCGAGUCGGUGC SEQ ID NO: 18 or an active portion thereof.
• tracrRNA (SEQ ID NO: 14) is used as a crRNA, the following tracrRNA is used:
• tracrRNA is used as a crRNA, the following tracrRNA is used:
• the gRNA is targeted to a site that is at least three or more mismatches different from any sequence in the rest of the genome in order to minimize off-target effects.
• RNA oligonucleotides such as locked nucleic acids (LNAs) have been demonstrated to increase the specificity of RNA-DNA hybridization by locking the modified oligonucleotides in a more favorable (stable) conformation.
• LNAs locked nucleic acids
• 2'-0-methyl RNA is a modified base where there is an additional covalent linkage between the 2' oxygen and 4' carbon which when incorporated into oligonucleotides can improve overall thermal stability and selectivity (Formula I).
• the tru-gRNAs disclosed herein may comprise one or more modified RNA oligonucleotides.
• the truncated guide RNAs molecules described herein can have one, some or all of the 17-18 or 17-19 nts 5 ' region of the guideRNA complementary to the target sequence are modified, e.g., locked (2'-0-4'-C methylene bridge), 5'-methylcytidine, 2'-0-methyl-pseudouridine, or in which the ribose phosphate backbone has been replaced by a polyamide chain (peptide nucleic acid), e.g., a synthetic ribonucleic acid.
• a polyamide chain peptide nucleic acid
• one, some or all of the nucleotides of the tru-gRNA sequence may be modified, e.g., locked (2'-0-4'-C methylene bridge), 5'- methylcytidine, 2'-0-methyl-pseudouridine, or in which the ribose phosphate backbone has been replaced by a polyamide chain (peptide nucleic acid), e.g., a synthetic ribonucleic acid.
• the single guide RNAs and/or crRNAs and/or tracrRNAs can include one or more Adenine (A) or Uracil (U) nucleotides on the 3 ' end.
• A Adenine
• U Uracil
• RNA-DNA heteroduplexes can form a more promiscuous range of structures than their DNA-DNA counterparts.
• DNA-DNA duplexes are more sensitive to mismatches, suggesting that a DNA- guided nuclease may not bind as readily to off-target sequences, making them comparatively more specific than RNA-guided nucleases.
• the guide RNAs usable in the methods described herein can be hybrids, i.e., wherein one or more deoxyribonucleotides, e.g., a short DNA oligonucleotide, replaces all or part of the gRNA, e.g., all or part of the complementarity region of a gRNA.
• This DNA-based molecule could replace either all or part of the gRNA in a single gRNA system or alternatively might replace all of part of the crRNA and/or tracrRNA in a dual crRNA/tracrRNA system.
• complementarity region should more reliably target the intended genomic DNA sequences due to the general intolerance of DNA-DNA duplexes to mismatching compared to R A-DNA duplexes.
• Methods for making such duplexes are known in the art, See, e.g., Barker et al, BMC Genomics. 2005 Apr 22;6:57; and Sugimoto et al, Biochemistry. 2000 Sep 19;39(37): 11270-81.
• one or both can be synthetic and include one or more modified (e.g., locked) nucleotides or deoxyribonucleotides .
• complexes of Cas9 with these synthetic gR could be used to improve the genome-wide specificity of the CRISPR/Cas9 nuclease system.
• the methods described can include expressing in a cell, or contacting the cell with, a Cas9 gRNA plus a fusion protein as described herein.
• the nucleic acid encoding the guide RNA can be cloned into an intermediate vector for transformation into prokaryotic or eukaryotic cells for replication and/or expression.
• Intermediate vectors are typically prokaryote vectors, e.g., plasmids, or shuttle vectors, or insect vectors, for storage or manipulation of the nucleic acid encoding the fusion proteins for production of the fusion proteins.
• the nucleic acid encoding the fusion proteins can also be cloned into an expression vector, for administration to a plant cell, animal cell, preferably a mammalian cell or a human cell, fungal cell, bacterial cell, or protozoan cell.
• a sequence encoding a fusion protein is typically subcloned into an expression vector that contains a promoter to direct transcription.
• Suitable bacterial and eukaryotic promoters are well known in the art and described, e.g., in Sambrook et al., Molecular Cloning, A Laboratory Manual (3d ed. 2001); Kriegler, Gene Transfer and Expression: A Laboratory Manual (1990); and Current Protocols in Molecular Biology (Ausubel et al, eds., 2010).
• Bacterial expression systems for expressing the engineered protein are available in, e.g., E. coli, Bacillus sp., and Salmonella (Palva et al, 1983, Gene 22:229-235).
• Kits for such expression systems are commercially available. Eukaryotic expression systems for mammalian cells, yeast, and insect cells are well known in the art and are also commercially available.
• the promoter used to direct expression of a nucleic acid depends on the particular application. For example, a strong constitutive promoter is typically used for expression and purification of fusion proteins.
• a constitutive or an inducible promoter can be used, depending on the particular use of the guide RNA.
• a preferred promoter for administration of the guide RNA can be a weak promoter, such as HSV TK or a promoter having similar activity.
• the promoter can also include elements that are responsive to transactivation, e.g., hypoxia response elements, Gal4 response elements, lac repressor response element, and small molecule control systems such as tetracycline-regulated systems and the RU-486 system (see, e.g., Gossen & Bujard, 1992, Proc. Natl. Acad. Sci. USA, 89:5547; Oligino et al, 1998, Gene Ther., 5:491-496; Wang et al, 1997, Gene Ther., 4:432-441; Neering et al, 1996, Blood, 88: 1147-55; and Rendahl et al, 1998, Nat. BiotechnoL, 16:757-761).
• elements that are responsive to transactivation e.g., hypoxia response elements, Gal4 response elements, lac repressor response element, and small molecule control systems such as tetracycline-regulated systems and the RU-486 system (see, e
• the expression vector typically contains a transcription unit or expression cassette that contains all the additional elements required for the expression of the nucleic acid in host cells, either prokaryotic or eukaryotic.
• Atypical expression cassette thus contains a promoter operably linked, e.g., to the nucleic acid sequence encoding the gRNA, and any signals required, e.g., for efficient polyadenylation of the transcript, transcriptional termination, ribosome binding sites, or translation termination.
• Additional elements of the cassette may include, e.g., enhancers, and heterologous spliced intronic signals.
• the particular expression vector used to transport the genetic information into the cell is selected with regard to the intended use of the gRNA, e.g., expression in plants, animals, bacteria, fungus, protozoa, etc.
• Standard bacterial expression vectors include plasmids such as pBR322 based plasmids, pSKF, pET23D, and commercially available tag-fusion expression systems such as GST and LacZ.
• Expression vectors containing regulatory elements from eukaryotic viruses are often used in eukaryotic expression vectors, e.g., SV40 vectors, papilloma virus vectors, and vectors derived from Epstein-Barr virus.
• eukaryotic vectors include pMSG, pAV009/A+, pMTO10/A+, pMAMneo-5, baculovirus pDSVE, and any other vector allowing expression of proteins under the direction of the SV40 early promoter, SV40 late promoter, metallothionein promoter, murine mammary tumor virus promoter, Rous sarcoma virus promoter, polyhedrin promoter, or other promoters shown effective for expression in eukaryotic cells.
• the vectors for expressing the guide RNAs can include RNA Pol III promoters to drive expression of the guide RNAs, e.g., the HI, U6 or 7SK promoters. These human promoters allow for expression of gRNAs in mammalian cells following plasmid transfection. Alternatively, a T7 promoter may be used, e.g., for in vitro transcription, and the RNA can be transcribed in vitro and purified. Vectors suitable for the expression of short RNAs, e.g., siRNAs, shRNAs, or other small RNAs, can be used. With the Cys4-based multiplex system described in Figure 4B, multiple gRNAs can be expressed in a single transcript (driven by a RNA Pol II or Pol III promoter) and then cleaved out from that larger transcript.
• RNA Pol III promoters to drive expression of the guide RNAs.
• Some expression systems have markers for selection of stably transfected cell lines such as thymidine kinase, hygromycin B phosphotransferase, and dihydrofolate reductase.
• High yield expression systems are also suitable, such as using a baculovirus vector in insect cells, with the gRNA encoding sequence under the direction of the polyhedrin promoter or other strong baculovirus promoters.
• the elements that are typically included in expression vectors also include a replicon that functions in E. coli, a gene encoding antibiotic resistance to permit selection of bacteria that harbor recombinant plasmids, and unique restriction sites in nonessential regions of the plasmid to allow insertion of recombinant sequences.
• Standard transfection methods are used to produce bacterial, mammalian, yeast or insect cell lines that express large quantities of protein, which are then purified using standard techniques (see, e.g., Colley et al, 1989, J. Biol. Chem., 264: 17619-22; Guide to Protein Purification, in Methods in Enzymology, vol. 182 (Deutscher, ed., 1990)). Transformation of eukaryotic and prokaryotic cells are performed according to standard techniques (see, e.g., Morrison, 1977, J. Bacteriol. 132:349-351; Clark-Curtiss & Curtiss, Methods in Enzymology 101 :347-362 (Wu et al, eds, 1983).
• Any of the known procedures for introducing foreign nucleotide sequences into host cells may be used. These include the use of calcium phosphate transfection, polybrene, protoplast fusion, electroporation, nucleofection, liposomes,
• microinjection naked DNA, plasmid vectors, viral vectors, both episomal and integrative, and any of the other well-known methods for introducing cloned genomic DNA, cDNA, synthetic DNA or other foreign genetic material into a host cell (see, e.g., Sambrook et al., supra). It is only necessary that the particular genetic engineering procedure used be capable of successfully introducing at least one gene into the host cell capable of expressing the gRNA.
• the present invention includes the vectors and cells comprising the vectors.
• RGNs CRISPR RNA-guided nucleases
• Example 1 The following materials and methods were used in Example 1.
• DNA oligonucleotides harboring variable 20 nt sequences for Cas9 targeting were annealed to generate short double-strand DNA fragments with 4 bp overhangs compatible with ligation into BsmBI-digested plasmid pMLM3636. Cloning of these annealed oligonucleotides generates plasmids encoding a chimeric +103 single-chain guide RNA with 20 variable 5 ' nucleotides under expression of a U6 promoter
• pMLM3636 and the expression plasmid pJDS246 (encoding a codon optimized version of Cas9) used in this study are both available through the non-profit plasmid distribution service Addgene (addgene.org/crispr-cas).
• U20S.EGFP cells harboring a single integrated copy of an EGFP-PEST fusion gene were cultured as previously described (Reyon et al, Nat Biotech 30, 460- 465 (2012)).
• 200,000 cells were Nucleofected with the indicated amounts of gRNA expression plasmid and pJDS246 together with 30 ng of a Td- tomato-encoding plasmid using the SE Cell Line 4D-NucleofectorTM X Kit (Lonza) according to the manufacturer's protocol. Cells were analyzed 2 days post- transfection using a BD LSRII flow cytometer. Transfections for optimizing gR A/Cas9 plasmid concentration were performed in triplicate and all other transfections were performed in duplicate.
• PCR reactions were performed using Phusion Hot Start II high-fidelity DNA polymerase (NEB). Most loci amplified successfully using touchdown PCR (98 °C, 10 s; 72-62 °C, -1 °C/cycle, 15 s; 72 °C, 30 s]10 cycles, [98 °C, 10 s; 62 °C, 15 s; 72 °C, 30 s]25 cycles). PCR for the remaining targets were performed with 35 cycles at a constant annealing temperature of 68 °C or 72 °C and 3% DMSO or 1M betaine, if necessary. PCR products were analyzed on a QIAXCEL capillary electrophoresis system to verify both size and purity. Validated products were treated with ExoSap-IT (Affymetrix) and sequenced by the Sanger method (MGH DNA Sequencing Core) to verify each target site.
• NEB Phusion Hot Start II high-fidelity DNA polymerase
• Lipofectamine LTX reagent according to the manufacturer's instructions (Life Technologies). Genomic DNA was harvested from transfected U20S.EGFP,
• HEK293, or K562 cells using the QIAamp DNA Blood Mini Kit (QIAGEN), according to the manufacturer's instructions.
• QIAGEN QIAamp DNA Blood Mini Kit
• PCR was then performed using these genomic DNAs as templates as described above and purified using Ampure XP beads (Agencourt) according to the manufacturer's instructions. T7EI assays were performed as previously described (Reyon et al, 2012, supra).
• EGFP enhanced green fluorescent protein
• the activities of nucleases targeted to a single integrated EGFP reporter gene can be quantified by assessing loss of fiuorescence signal in human U20S.EGFP cells caused by inactivating frameshift insertion/deletion (indel) mutations introduced by error prone non-homologous end-joining (NHEJ) repair of nuclease-induced double- stranded breaks (DSBs) (Fig. 2B).
• sgRNAs three -100 nt single gRNAs targeted to different sequences within EGFP were used, as follows:
• EGFP Site 1 GGGCACGGGCAGCTTGCCGGTGG (SEQ ID NO : 1 )
• EGFP Site 2 GATGCCGTTCTTCTGCTTGTCGG (SEQ ID NO:2)
• Each of these sgRNAs can efficiently direct Cas9-mediated disruption of EGFP expression (see Example le and 2a, and FIGs. 3E (top) and 3F (top)).
• variant sgRNAs were generated for each of the three target sites harboring Watson-Crick transversion mismatches at positions 1 through 19 (numbered 1 to 20 in the 3' to 5' direction; see Fig. 1) and the abilities of these various sgR As to direct Cas9-mediated EGFP disruption in human cells tested (variant sgRNAs bearing a substitution at position 20 were not generated because this nucleotide is part of the U6 promoter sequence and therefore must remain a guanine to avoid affecting expression.)
• target site #1 was particularly sensitive to a mismatch at position 2 whereas target site #3 was most sensitive to mismatches at positions 1 and 8.
• variant sgRNAs were constructed bearing increasing numbers of mismatched positions ranging from positions 19 to 15 in the 5' end of the gRNA targeting region (where single and double mismatches appeared to be better tolerated).
• sgRNAs that target three different sites in the VEGFA gene, one in the EMX1 gene, one in the RNF2 gene, and one in the FANCF gene were used. These six sgRNAs efficiently directed Cas9-mediated indels at their respective endogenous loci in human U20S.EGFP cells as detected by T7
• T7EI Endonuclease I assay
• U20S.EGFP cells The loci assessed included all genomic sites that differ by one or two nucleotides as well as subsets of genomic sites that differ by three to six nucleotides and with a bias toward those that had one or more of these mismatches in the 5' half of the gRNA targeting sequence.
• T7EI assay four off-target sites (out of 53 candidate sites examined) for VEGFA site 1, twelve (out of 46 examined) for VEGFA site 2, seven (out of 64 examined) for VEGFA site 3 and one (out of 46 examined) for the EMX1 site were readily identified. No off-target mutations were detected among the 43 and 50 potential sites examined for the RNF2 or FANCF genes, respectively.
• the rates of mutation at verified off-target sites were very high, ranging from 5.6% to 125% (mean of 40%) of the rate observed at the intended target site.
• These bona fide off-targets included sequences with mismatches in the 3' end of the target site and with as many as a total of five mismatches, with most off-target sites occurring within protein coding genes.
• DNA sequencing of a subset of off-target sites provided additional molecular confirmation that indel mutations occur at the expected RGN cleavage site (Figs. 8A-C).
• NHEJ-mediated indel mutations at their intended on-target site in these two additional human cell lines (as assessed by T7EI assay), albeit with somewhat lower mutation frequencies than those observed in U20S.EGFP cells.
• Assessment of the 24 off-target sites for these four RGNs originally identified in U20S.EGFP cells revealed that many were again mutated in HEK293 and K562 cells with frequencies similar to those at their corresponding on-target site.
• DNA sequencing of a subset of these off-target sites from HEK293 cells provided additional molecular evidence that alterations are occurring at the expected genomic loci.
• Single guide RNAs were generated for three different sequences (EGFP SITES 1-3, shown above) located upstream of EGFP nucleotide 502, a position at which the introduction of frameshift mutations via non-homologous end- joining can robustly disrupt expression of EGFP (Maeder, M.L. et al, Mol Cell 31, 294-301 (2008); Reyon, D. et al, Nat Biotech 30, 460-465 (2012)).
• gRNA-expressing plasmid amounts (12.5 to 250 ng) was initially trans fected together with 750 ng of a plasmid expressing a codon-optimized version of the Cas9 nuclease into our U20S.EGFP reporter cells bearing a single copy, constitutively expressed EGFP-PEST reporter gene. All three RGNs efficiently disrupted EGFP expression at the highest concentration of gRNA plasmid (250 ng) (Fig. 3E (top)).
• RGNs for target sites #1 and #3 exhibited equivalent levels of disruption when lower amounts of gRNA-expressing plasmid were transfected whereas RGN activity at target site #2 dropped immediately when the amount of gRNA-expressing plasmid transfected was decreased (Fig. 3E (top)).
• the amount of Cas9-encoding plasmid (range from 50 ng to 750 ng) transfected into our U20S.EGFP reporter cells was titrated EGFP disruption assayed. As shown in Fig. 3F (top), target site #1 tolerated a three-fold decrease in the amount of Cas9-encoding plasmid transfected without substantial loss of EGFP disruption activity. However, the activities of RGNs targeting target sites #2 and #3 decreased immediately with a three-fold reduction in the amount of Cas9 plasmid transfected (Fig. 3F (top)).
• Off-target sites for each of the six RGNs targeted to the VEGFA, RNF2, FANCF, and EMX1 genes and the three RGNs targeted to EGFP Target Sites #1, #2 and #3 were identified in human genome sequence build GRCh37. Mismatches were only allowed for the 20 nt region to which the gRNA anneals and not to the PAM sequence.
• Example 2 Using pairs of guideRNAs with FokI-dCas9 fusion proteins
• Monomeric CRISPR-Cas9 nucleases are widely used for targeted genome editing but can induce unwanted off-target mutations with high frequencies.
• This example describes new dimeric RNA-guided Fokl Nucleases (RFNs) that recognize an extended, double-length sequence and that strictly depend on two single guide RNAs (gRNAs) for cleavage activity. RFNs can robustly edit DNA sequences in endogenous human genes with high efficiencies. Additionally, a method for expressing gRNAs bearing any 5 ' end nucleotide is described, a critical advance that gives dimeric RFNs a useful targeting range.
• RFNs RNA-guided Fokl Nucleases
• monomeric Cas9 nickases In direct comparisons, monomeric Cas9 nickases generally induce unwanted indels and unexpected focal point mutations with higher frequencies than RFNs directed by a matched single gRNA.
• RFNs combine the ease of CRISPR RNA-based targeting with the specificity enhancements of dimerization and provide an important new platform for research and therapeutic applications that require highly precise genome editing.
• Plasmids encoding single or multiplex gRNAs were assembled in a single-step ligation of annealed target site oligosduplexes (Integrated DNA Technologies) and a constant region oligoduplex (for multiplex gRNAs) with BsmBI-digested Csy4- flanked gRNA backbone (pSQT1313; Addgene).
• Multiplex gRNA encoding plasmids were constructed by ligating: 1) annealed oligos encoding the first target site, 2) phosphorylated annealed oligos encoding crRNA, tracrRNA, and Csy4-binding site, and 3) annealed oligos encoding the second target site, into a U6-Csy4site-gRNA plasmid backbone digested with BsmBI Type lis restriction enzyme.
• Csy4 RNA binding sites were attached to the 3' and 5' ends of a gRNA sequence and expressed with Cas9 in cells.
• the Csy4 RNA binding site sequence ' GUUC ACUGCCGUAUAGGC AGCUAAGAAA' was fused to the 5' and 3' end of the standard gRNA sequence.
• This sequence is a multiplex gRNA sequence flanked by Csy4 sites (underlined). Functionally, encoding these in multiplex on one transcript should have the same result as encoding them separately. Although all pairs of Csy4-flanked sgRNAs were expressed in a multiplex context in the experiments described herein, the sgRNAs can be encoded in multiplex sgRNAs separated by Csy4 sites encoded on one transcript as well as individual sgRNAs that have an additional Csy4 sequence.
• the first N20 sequence represents the sequence complementary to one strand of the target genomic sequence
• the second N20 sequence represents the sequence complementary to the other strand of the target genomic sequence.
• a plasmid encoding the Csy4 recognition site containing gR A was co- transfected with plasmid encoding Cas9 and Csy4 proteins separated by a '2A' peptide linkage.
• the results showed that gR As with Csy4 sites fused to the 5' and 3 ' ends remained capable of directing Cas9-mediated cleavage in human cells using the U20S-EGFP disruption assay previously described.
• Csy4 R A binding sites can be attached to 3 ' end of a gRNA sequence and complexes of these Csy4 site- containing gRNAs with Cas9 remain functional in the cell.
• the sequences of the FokI-dCas9 fusions are shown below, and include a GGGGS (SEQ ID NO:23) linker (underlined) between the Fokl and dCas9 and a nuclear localization sequence.
• FokI-dCas9 amino acid sequence (FokI-G4S-dCas9-nls-3XFLAG) MQLVKSELEEKKSELRHKLKYVPHEYIELIEIARNSTQDRILEMKVMEFFMKVYGYR GKHLGGSRKPDGAIYTVGSPIDYGVIVDTKAYSGGYNLPIGQADEMQRYVEENQTRN KHINPNEWWKVYPSSVTEFKFLFVSGHFKGNYKAQLTRLNHITNCNGAVLSVEELLI GGEMIKAGTLTLEEVRRKFNNGEINFGGGGSDKKYS IGLAIGTNSVGWAVITDEYKV PSKKFKVLGN DRHS IKKNLIGALLFDSGE AEATRLKRTARRRYTRRKNRICYLQE IFSNEMAKVDDSFFHRLEESFLVEEDKKHERHPIFG IVDEVAYHEKYP IYHLRKK LVDS DKADLRLIYLALAHMI
• FokI-dCas9 nucleotide sequence (FokI-G4S-dCas9-nls-3XFLAG)
• U20S.EGFP cells were cultured in the presence of 400 ⁇ g/ml of G418.
• U20S cells and U20S.EGFP cells were transfected using the DN-100 program of a Lonza 4D-Nucleofector according to the manufacturer's instructions.
• 750 ng of pCAG-Csy4-FokI-dCas9-nls nuclease plasmid and 250 ng of gRNA encoding plasmids were transfected together with 50 ng tdTomato expression plasmid (Clontech) as a transfection control.
• tdTomato expression plasmid (Clontech)
• U20S.EGFP cells 975 ng of human codon optimized pCAG-Csy4-T2A-nls-hFokI- dCas9-nls (SQT1601) or pCAG-Cas9-D10A nickase (NW3) were transfected along with 325 ng of gRNA vector and 10 ng of Td tomato expression plasmid and analyzed 3 days after transfection.
• HEK293 cells were transfected with 750 ng of nuclease plasmid, 250 ng of gRNA expression plasmid and 10 ng of Td tomato, using
• the EGFP disruption assay was performed as previously described (see Example 1 and Reyon et al, Nat Biotech 30, 460-465 (2012)) using U20S.EGFP reporter cells. Cells were assayed for EGFP and tdTomato expression using an BD Biosciences LSR II or Fortessa FACS analyzer.
• T7E1 assays were performed as previously described (Reyon et al, Nat Biotech 30, 460-465 (2012)). Briefly, genomic DNA was isolated 72 hours post transfection using the Agencourt DNAdvance Genomic DNA Isolation kit (Beckman Coulter Genomics) according to the manufacturer's instructions with a Sciclone G3 liquid-handling workstation (Caliper). PCR reactions to amplify genomic loci were performed using Phusion Hot- start Flex DNA polymerase (New England Biolabs).
• Samples were amplified using a two-step protocol (98 °C, 30 sec; (98 °C, 7 sec; 72 °C, 30 sec) x 35; 72 °C, 5 min) or a touchdown PCR protocol ((98 °C, 10 s; 72-62 °C, -1 °C/cycle, 15 s; 72 °C, 30 s) 10 cycles, (98 °C, 10 s; 62 °C, 15 s; 72 °C, 30 s) 25 cycles).
• 200 ng of purified PCR amplicons were denatured, hybridized, and treated with T7 Endonuclease I (New England Biolabs). Mutation frequency was quantified using a Qiaxcel capillary electrophoresis instrument (Qiagen) as previously described (Reyon et al, Nat Biotech 30, 460-465 (2012)).
• Short 200-350 bp PCR products were amplified using Phusion Hot- start FLEX DNA polymerase. PCR products were purified using Ampure XP beads (Beckman Coulter Genomics) according to manufacturer's instructions. Dual-indexed TruSeq Illumina deep sequencing libraries were prepared using a high-throughput library preparation system (Kapa Biosystems) on a Sciclone G3 liquid-handling workstation. Final adapter-ligated libraries were quantified using a Qiaxcel capillary electrophoresis instrument (Qiagen). 150 bp paired end sequencing was performed on an Illumina MiSeq Sequencer by the Dana-Farber Cancer Institute Molecular Biology Core.
• MiSeq paired-end reads were mapped to human genome reference GChr37 using bwa. Reads with an average quality score >30 were analyzed for insertion or deletion mutations that overlapped the intended target or candidate off-target nuclease binding site. Mutation analyses were conducted using the Genome Analysis Toolkit (GATK) and Python.
• GATK Genome Analysis Toolkit
• a target-site matching algorithm was implemented that looks for matches with less than a specified number of mismatches in a sliding window across the human genome.
• Example 2a Rationale for designing dimeric RNA-guided nucleases
• Example 2b Multiplex expression of gRNAs without 5 '-end nucleotide limitations
• the targeting range for a dimeric RNA-guided nuclease would be low using existing gRNA expression methods.
• Two sequence requirements typically restrict the targeting range of a dCas9 monomer: the requirement for a PAM sequence of 5'- NGG that is specified by the dCas9 and a requirement for a G nucleotide at the 5' end of the gRNA imposed by the use of a U6 promoter in most expression vectors. If, however, the requirement for the 5 ' G in the gRNA could be relieved, then the targeting range would improve by 16-fold.
• a plasmid was constructed from which two gRNAs, each flanked by cleavage sites for the Csy4 ribonuclease (Haurwitz et al, Science 329, 1355-1358 (2010)), can be expressed within a single RNA transcribed from a U6 promoter (Fig. 4B). Csy4 would be expected to process this transcript thereby releasing the two gRNAs.
• each processed gRNA should retain a Csy4 recognition site on its 3' end with a Csy4 protein bound to that site (Fig. 4B).
• gRNAs with any 5' nucleotide. This system was tested by using it to express two gRNAs targeted to sites within the EGFP reporter gene.
• Example 2c Construction and optimization of dimeric RNA-guided nucleases Two different hybrid proteins harboring the Fokl nuclease domain and the dCas9 protein were constructed: one in which the Fokl nuclease domain is fused to the carboxy-terminus of dCas9 (dCas9-FokI) and the other in which it is fused to the amino-terminus (FokI-dCas9) (Fig. 5A).
• the dCas9-FokI protein is analogous in architecture to ZFNs and TALENs (Fig. 5A).
• the dCas9-FokI protein did not show detectable EGFP disruption activity when co-expressed with any of the 60 gRNA pairs in human U20S.EGFP cells (Fig. 5E).
• screening of the FokI-dCas9 protein with the same 60 gRNA pairs did reveal EGFP disruption activity on target sites composed of half-sites in the PAM out orientation and with spacer lengths of 13 to 17 bps and of 26 bps (approximately one turn of the DNA helix more than the 13-17 bp spacer lengths) (Fig. 5B).
• FokI-dCas9 can be directed by two appropriately positioned gRNAs to efficiently cleave a full-length target site of interest.
• the complex of two FokI-dCas9 fusions and two gRNAs are referred to herein as RNA-guided Fokl Nucleases (RFNs).
• gRNA pairs were designed for 12 different target sites in nine different human genes (Table 2). Eleven of the 12 RFNs tested introduced indels with high efficiencies (range of 3 to 40%) at their intended target sites in human U20S.EGFP cells as judged by T7EI assay (Table 2). Similar results were obtained with these same 12 RFN pairs in HEK293 cells (Table 2). Sanger sequencing of successfully targeted alleles from U20S.EGFP cells revealed the introduction of a range of indels (primarily deletions) at the expected cleavage site (Fig. 5F). The high success rate and high efficiencies of modifications observed in two different human cell lines demonstrate the robustness of RFNs for modifying endogenous human genes.
• Example 2d RFNs possess extended specificities for their cleavage sites To test whether RFNs possess enhanced recognition specificities associated with dimerization, whether these nucleases strictly depend upon the presence of both gRNAs in a pair was examined. In an ideal dimeric system, single gRNAs should not be able to efficiently direct FokI-dCas9-induced indels. To perform an initial test, two pairs of gRNAs directed to two target sites in EGFP were used that had been shown to efficiently direct FokI-dCas9-induced indels to their target sites (EGFP sites 47 and 81) in human U20S.EGFP cells (Fig. 5C).
• Example 2e Monomeric Cas9 nickases induce higher rates of mutagenesis than single gRNA/FokI-dCas9 complexes
• FokI-dCas9 and Cas9 nickase were compared in the presence of a single gRNA at six dimeric human gene target sites (a total of 12 half-sites; Table 4). These particular sites were chosen because monomeric Cas9 nickases directed by just one and/or the other gRNA in a pair could induce indel mutations at these targets.
• Table 4 the activities of FokI-dCas9 or Cas9 nickase were assessed in the presence of both or only one or the other gRNAs.
• Example 2f Dimeric RFNs possess a high degree of specificity
• Dimeric RFNs directed by two gRNAs are not expected to induce appreciable off-target mutations in human cells.
• RFNs directed by a pair of gRNAs to cleave a full-length sequence composed of two half-sites, would be expected to specify up to 44 bps of DNA in the target site. A sequence of this length will, by chance, almost always be unique (except in certain circumstances where the target might lie in duplicated genome sequence).
• the most closely matched sites in the genome to this full-length site should, in most cases, possess a large number of mismatches, which in turn would be expected to minimize or abolish cleavage activity by an RFN dimer.
• VEGFA-2 1 4 9 99 447 1675 5608 18599
• VEGFA-3 1 20 120 623 2783 References

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