Compositions and methods for selection of nucleic acids
Methods are provided for reducing the complexity of a population of nucleic acids prior to performing an analysis of the nucleic acids, e.g., sequence analysis. The methods result in a subset of the initial population enriched for a target region, which is typically located within one or more target fragments. The methods are particularly useful for analyzing populations having a high degree of complexity, e.g., chromosomal-derived DNA, whole genomic DNA, or mRNA populations.
1. A method for enrichment of a target region in a nucleic acid sample comprising:
a) obtaining a nucleic acid sample comprising a mixture of double-stranded nucleic acid fragments, wherein a subset of fragments in the mixture comprises the target region;
b) digesting the nucleic acid sample with a first endonuclease and a second endonuclease to produce a population of double-stranded nucleic acid fragments, wherein the first endonuclease cleaves a particular nucleotide sequence that is upstream of the target region and the second endonuclease cleaves a particular nucleotide sequence that is downstream of the target region;
c) ligating stem-loop adapters to the population of double-stranded nucleic acid fragments to produce a ligated sample; and
d) treating the ligated sample with: (i) one or more third endonucleases that do not cleave stem-loop ligated double-stranded nucleic acid fragments that include the target region, and (ii) one or more exonucleases that digest double-stranded nucleic acid fragments cleaved by the one or more third endonucleases, having one stem-loop adapter ligated thereto, or having no stem-loop adapter ligated thereto, thereby enriching for the target region in the nucleic acid sample.
2. The method of claim 1 , wherein a primer binding sequence is present within the stem-loop adapter.
3. The method of claim 2 , further comprising hybridizing a primer to the primer binding sequence in the enriched double-stranded nucleic acid fragments and exposing the primer-hybridized double-stranded nucleic acid fragments to a polymerase enzyme to generate a polymerase complex.
4. The method of claim 3 , further comprising exposing the polymerase complex to a capture-hook oligonucleotide attached to a magnetic bead to selectively capture the polymerase complex.
5. The method of claim 4 , wherein the capture-hook oligonucleotide only captures an active polymerase complex by binding to a region of the nucleic acid in the polymerase complex that has been rendered single-stranded by the polymerase enzyme.
6. The method of claim 1 , further comprising performing template-directed sequencing-by-synthesis on the enriched nucleic acid fragments.
7. The method of claim 6 , wherein the template-directed sequencing-by-synthesis generates redundant sequence information from single molecules of the enriched nucleic acid fragments.
8. The method of claim 1 , further comprising isolating fragments having an approximate size of a double-stranded nucleic acid fragment comprising the target region generated by digestion with the first endonuclease and a second endonuclease prior to the ligating step.
9. The method of claim 1 , wherein the first endonuclease and the second endonuclease are selected from the group consisting of: a type II restriction endonuclease, a type IIs restriction endonuclease, an engineered endonuclease, and any combination thereof.
10. The method of claim 9 , wherein the engineered endonuclease is an engineered zinc finger DNA-binding protein endonuclease.
11. The method of claim 9 , wherein the first endonuclease and the second endonuclease are engineered endonucleases.
12. The method of claim 1 , wherein the first endonuclease, the second endonuclease, or both leave ends with single-stranded overhangs.
13. The method of claim 12 , wherein:
the first endonuclease leaves a first single-stranded overhang and the second endonuclease leaves a second single-stranded overhang, wherein the first single-stranded overhang and the second single-stranded overhang are different; and
the stem-loop adapters comprise first stem-loop adapters and second stem-loop adapters, wherein the first stem-loop adapters comprise a single-stranded overhang that is complementary to the first single-stranded overhang and the second stem-loop adapters comprise a single-stranded overhang that is complementary to the second single-stranded overhang.
14. The method of claim 1 , wherein the first endonuclease, the second endonuclease, or both leave blunt ends.
15. The method of claim 1 , wherein the target region comprises repetitive sequences.
16. The method of claim 15 , wherein the repetitive sequences are repeat sequences associated with a genetic disorder.
17. The method of claim 16 , wherein the genetic disorder is selected from the group consisting of: fragile X syndrome, fragile X-associated tremor/ataxia syndrome (FXTAS), amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), Parkinson's disease, autism, cancer, myotonic dystrophy, ataxia, epilepsy, and Huntington's disease.
18. The method of claim 1 , wherein multiple different target regions are enriched in the nucleic acid sample.