Full interrogation of nuclease DSBs and sequencing (FIND-seq)

1. A library of covalently closed DNA fragments, the library obtained by a method comprising:

providing DNA;

randomly shearing the DNA to a defined average length to provide a population of DNA fragments;

preparing the population of DNA fragments for end-ligation;

ligating to the ends of the fragments a first hairpin adapter comprising a single stranded hairpin loop region comprising at least a single deoxyuridine and a first primer site, to prepare a first population of ligated fragments;

purifying the ligated fragments using an exonuclease, to prepare a population of purified ligated fragments;

treating the purified ligated fragments with a nuclease to induce double stranded breaks, including site-specific breaks, of the DNA;

optionally end-repairing and then A-tailing the resulting ends; and

ligating a second hairpin adapter comprising a first region of 10-20 nucleotides; a second region of 40-60 nucleotides that forms one or more single-stranded hairpin loops and comprises a second primer compatible for use with the first primer site in PCR priming and/or sequencing; and a third region of 10-20 nucleotides that is complementary to the first region and that also contains a single deoxyuridine nucleotide between the second and third regions, to create a population wherein the DNA fragments that were cleaved by the nuclease have a first and second hairpin adapter ligated to their respective ends, thereby producing a library of covalently closed DNA fragments,

wherein one end was created by a nuclease-induced double stranded break in the DNA,

wherein the first hairpin adapter comprises:

a first region of 10-20 nucleotides;

a second region of 45-65 nucleotides that forms one or more single-stranded hairpin loops and comprises a first primer site compatible for use in PCR priming and/or sequencing; and

a third region of 10-20 nucleotides that is complementary to the first region, with a single deoxyuridine nucleotide between the first and second regions,

wherein purifying the ligated fragments using an exonuclease comprises contacting the sample with one or more exonucleases, sufficient to degrade any DNA molecules that lack the first hairpin adapter ligated to both of their ends, and

wherein preparing the population of DNA fragments for end-ligation comprises end-repairing and then A-tailing the sheared DNA.

2. The library of claim 1 , wherein treating the purified ligated fragments with a nuclease to induce double stranded breaks comprises contacting the sample with a Cas9 nuclease complexed with a specific guide RNA (gRNA).

3. The library of claim 1 , wherein the nuclease that induces double stranded breaks is selected from the group consisting of meganucleases, MegaTALs, zinc-finger nucleases, transcription activator effector-like nucleases (TALEN), and Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas RNA-guided nucleases (CRISPR/Cas RGNs).

4. The library of claim 1 , wherein the DNA is randomly sheared to an average length of 200-1000 bps.

5. The library of claim 1 , wherein the DNA is genomic DNA isolated from a mammalian, plant, bacterial, or fungal cell.

6. The library of claim 1 , wherein the DNA is synthetic.

7. The library of claim 1 , wherein the first primer site in the first hairpin adapter comprises a next generation sequencing primer site, a randomized DNA barcode or unique molecular identifier (UMI).

8. A library of DNA fragments, the library obtained by a method comprising:

contacting the library of covalently closed DNA fragments of claim 1 with uracil DNA glycosylase (UDG) and/or endonuclease VIII to nick the DNA at the deoxyuridine, thereby producing a library of DNA fragments.