Evaluation and improvement of nuclease cleavage specificity
Engineered nucleases are promising tools for genome manipulation and determining off-target cleavage sites of these enzymes is of great interest. This disclosure provides in vitro selection methods that interrogate 10 11 DNA sequences for their ability to be cleaved by active nucleases, e.g., ZFNs and TALENs. The method revealed hundreds of thousands of DNA sequences that can be cleaved in vitro by two ZFNs, CCR5-224 and VF2468, which target the endogenous human CCR5 and VEGF-A genes, respectively. Analysis of the identified sites in cultured human cells revealed CCR5-224-induced mutagenesis at nine off-target loci. This disclosure provides an energy compensation model of ZFN specificity in which excess binding energy contributes to off-target ZFN cleavage. It was also observed that TALENs can achieve cleavage specificity similar to or higher than that observed in ZFNs.
1. A library of synthetic nucleic acid molecules comprising a plurality of nucleic acid molecules,
wherein each of the synthetic nucleic acid molecules comprises multiple copies of a DNA sequence linked in series, wherein each of the multiple copies of the DNA sequence linked in series in each of the synthetic nucleic acid molecules is the same and has the following structure:
5′-[(candidate nuclease target site)-(constant insert sequence)] x -3′, wherein x is at least 5;
wherein the nucleotide sequence of the constant insert sequence in each of the synthetic nucleic acid molecules is the same; and
wherein the candidate nuclease target site of each of the synthetic nucleic acid molecules of the library comprises the following structure:
5′-[left-half site]-[spacer sequence]-[right-half site]-3′ (LSR) structure, and wherein the nucleotide sequence of the LSR structure of each of the synthetic nucleic acid molecules is the same.
2. The library of claim 1 , wherein the left-half site and the right-half site comprise different nucleic acid sequences.
3. The library of claim 1 , wherein the left-half site and/or the right-half site are/is 10-18 nucleotides long.
4. The library of claim 1 , wherein some of the synthetic nucleic acid molecules of the library comprise the candidate nuclease target site that can be cleaved by a nuclease comprising a FokI cleavage domain.
5. The library of claim 1 , wherein some of the synthetic nucleic acid molecules of the library comprise the candidate nuclease target site that can be cleaved by a Zinc Finger Nuclease (ZFN) or a Transcription Activator-Like Effector Nuclease (TALEN).
6. The library of claim 1 , wherein the library comprises at least 10 5 different synthetic nucleic acid molecules.
7. The library of claim 1 , wherein the library of synthetic nucleic acid molecules comprises nucleic acid molecules having a molecular weight of at least 5 kDa.
8. The library of claim 1 , wherein the left-half site is a partially randomized left-half site, the right-half site is a partially randomized right-half site, and/or the spacer sequence is a partially randomized spacer sequence.
9. The library of claim 8 , wherein the partially randomized left-half site and/or the partially randomized right-half site are/is based on a known target site of a nuclease of interest.
10. The library of claim 9 , wherein the nuclease of interest is a ZEN, a TALEN, or a derivative thereof.
11. The library of claim 8 , wherein the partially randomized left-half site and/or the partially randomized right-half site differ/differs from a consensus site by more than 5% on average.
12. The library of claim 8 , wherein the partially randomized left-half site and/or the partially randomized right-half site differ/differs from a consensus site by no more than 10% on average.
13. The library of claim 8 , wherein the partially randomized left-half site and/or the partially randomized right-half site differ/differs from a consensus site by no more than 15% on average.
14. The library of claim 1 , wherein the spacer sequence is a randomized spacer sequence.
15. The library of claim 1 , wherein the candidate nuclease target site is located within a genomic sequence.
16. The library of claim 15 , wherein the genomic sequence is known to be associated with a disease or disorder.
17. The library of claim 16 , wherein the disease or disorder is human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS), or a proliferative disease.
18. The library of claim 15 , wherein the genomic sequence is a C-C chemokine receptor type 5 (CCRS5) sequence or vascular endothelial growth factor type A (VEGFA) sequence.
19. The library of claim 1 , wherein each of the synthetic nucleic acid molecules of the library comprises at least ten copies of the DNA sequence linked in series.
20. The library of claim 1 , wherein each of the synthetic nucleic acid molecules of the library comprises at least 100 copies of the DNA sequence linked in series.
21. The library of claim 8 , wherein the partially randomized left-half site and/or the partially randomized right-half site differ/differs from a consensus site by one, two, three, four, or five nucleotide residue/residues.
22. The library of claim 8 , wherein the partially randomized left-half site and/or the partially randomized right-half site differ/differs from a consensus site by three nucleotide residues.
23. The library of claim 1 , wherein the synthetic nucleic acid molecules of the library comprise other candidate nuclease target sites that can be cleaved by an enediyne, a dynemicin, a neocarzinostatin, a calicheamicin, an esperamicin, or a bleomycin.