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) digesting the nucleic acid sample with a restriction enzyme that cuts a defined distance from its recognition site to produce a population of double-stranded nucleic acid fragments, wherein fragments containing the target region have known single-stranded overhangs on each end, each overhang being different;
b) ligating two types of stem-loop adapters to the population of nucleic acid fragments, wherein one type of stem-loop adapter has a single-stranded overhang sequence complementary to a first of the known single-strand overhangs at one end of the fragment comprising the target region, and the other type of stem-loop adapter has a single-stranded overhang sequence complementary to a second of the known single-stranded overhangs on the other end of the fragment comprising the target region;
c) treating the sample with one or more exonucleases to digest the double-stranded nucleic acid fragments that have one or no stem-loop adapter linked thereto, thus enriching for the target region in the nucleic acid sample.
2. The method of claim 1 , wherein one or more restriction enzymes chosen to cleave fragments other than the fragments comprising the target region are added to the population of fragments prior to or during said treating.
3. The method of claim 1 , wherein a primer binding sequence is present within at least one of the adapters.
4. The method of claim 3 , wherein a printer is bound to the primer binding sequence.
5. The method of claim 4 , wherein the prim is also complementary to a portion of the target region.
6. The method of claim 5 , wherein the primer comprises modified bases that hybridize to the portion of the target region.
7. The method of claim 1 , further comprising performing template-directed sequencing-by-synthesis on fragments not digested in step c.
8. The method of claim 7 , wherein the template-directed sequencing-by-synthesis generates redundant sequence information from single molecules of the fragments not digested in step c.
9. The method of claim 1 , therein the sample nucleic acids are not amplified subsequent to the digestion.
10. The method of claim 1 , wherein the sample nucleic acids are subjected to rolling-circle amplification prior to the ligating.
11. The method of claim 1 , wherein the sample nucleic acids are native nucleic acids.
12. The method of claim 11 , wherein the native nucleic acids are genomic DNA.
13. The method of claim 1 , wherein the sample nucleic acids are amplified nucleic acids.