Methods and compositions for enrichment of target polynucleotides
High-fidelity, high-throughput nucleic acid sequencing enables healthcare practitioners and patients to gain insight into genetic variants and potential health risks. However, previous methods of nucleic acid sequencing often introduces sequencing errors (for example, mutations that arise during the preparation of a nucleic acid library, during amplification, or sequencing). Provided herein are methods and compositions for sequencing nucleic acids. Further provided are methods of identifying an error in a nucleic acid sequence.
1. A nucleic acid sequencing library, comprising a plurality of amplified primer extension products prepared according to a method comprising:
(a) ligating an adapter to each end of a target nucleic acid duplex, wherein the target nucleic acid duplex comprises cell-free DNA,
wherein the target nucleic acid duplex comprises first and second nucleic acid strands that are complementary to one another,
wherein each of the adaptors comprises: (i) a double stranded region that is ligated to one end of the target nucleic acid duplex; and (ii) first and second single stranded regions,
wherein the first single stranded region comprises an amplification primer binding sequence S2 and a 3′ end, and
wherein the second single stranded region comprises, from 5′ to 3′, a 5′ end, a first grafting sequence P5 for attachment to a flow cell, a first sample index sequence SI5, a molecular barcode A, and a first sequencing primer binding site S1, or wherein the second single stranded region comprises, from 5′ to 3′, a 5′ end, a first grafting sequence P5 for attachment to a flow cell, a molecular barcode A, a first sample index sequence SI5, a first sequencing primer binding site S1,
wherein the molecular barcodes on the adaptors are the same or different;
(b) amplifying the ligated nucleic acid produced in (a) using a first amplification primer that comprises a nucleic acid sequence that is complementary to the amplification primer binding sequence S2 and a second amplification primer that is complementary to at least a portion of the first grafting sequence P5,
wherein the first amplification primer comprises a 5′ phosphate group, and
wherein the second amplification primer comprises one or more nucleotide(s) at or near the 5′ end comprising a modification to prevent nucleic acid strand degradation by an exonuclease enzyme;
(c) digesting the amplified nucleic acids produced in (b) with a 5′→3′ exonuclease, thereby yielding single stranded nucleic acid products that comprise the sequence of either the first or second strand of the target nucleic acid duplex and the modified nucleotide(s) at or near the 5′ end, wherein the modified nucleotide(s) comprises at least one phosphorothioate modified nucleotides;
(d) hybridizing and extending a primer that comprises:
(i) a probe sequence that is complementary to a portion of the target nucleic acid sequence of the first or second strand; and
(ii) a second sequencing primer binding sequence S3, thereby producing primer extension products that comprise the first grafting sequence P5 at the 3′ end and second sequencing primer binding sequence S3 at the 5′ end; and
(e) amplifying the primer extension products, using: (i) a third amplification primer that comprises, from 5′ to 3′, a second grafting sequence P7, a second sample index sequence SI7, and a sequence that is complementary to the second sequencing binding sequence S3; and
(ii) a fourth amplification primer that comprises a sequence that is complementary to the first grafting sequence P5, thereby producing amplified primer extension products and their complements.
2. The nucleic acid sequencing library according to claim 1 , wherein the target nucleic acid duplex in step (a) is derived from about 1 ng or more of fragmented DNA.
3. The nucleic acid sequencing library according to claim 1 wherein the amplified nucleic acid product of step (b) comprises about 200 ng or more of amplified ligated nucleic acid.
4. The nucleic acid sequencing library according to claim 1 , wherein the modified nucleotide(s) in the second amplification primer in step (b) comprise a 5′ phosphorothioate group.
5. The nucleic acid sequencing library according to claim 4 , wherein the second amplification primer comprises five or more phosphorothioate modified nucleotides at or near the 5′ end of the primer.
6. The nucleic acid sequencing library according to claim 1 , wherein the exonuclease in step (c) is a double-stranded exonuclease.
7. The nucleic acid sequencing library according to claim 6 , wherein the exonuclease is a lambda exonuclease.
8. The nucleic acid sequencing library according to claim 1 , wherein the molecular barcode in the second single-stranded region of the adaptor is about 5 to about 15 nucleotides in length.
9. The nucleic acid sequencing library according to claim 1 , wherein the amplifying in step (b) comprises polymerase chain reaction (PCR) or a linear amplification method.
10. The nucleic acid sequencing library according to claim 1 , wherein the amplifying in step (e) comprises PCR or a linear amplification method.
11. The nucleic acid sequencing library according to claim 1 , comprising repeating step (d) with a plurality of different probes, in different reaction mixtures, to produce a plurality of primer extension products that will provide different start points for sequencing of the target nucleic acid sequence.
12. The nucleic acid sequencing library according to claim 1 , wherein the cell-free DNA comprise cell-free tumor DNA or cell-free fetal DNA.
13. The nucleic acid sequencing library according to claim 1 , wherein the target nucleic acid duplex is enriched from a nucleic acid library.
14. The nucleic acid sequencing library according to claim 13 , wherein the target nucleic acid duplex is enriched using a set of capture probes for a region of interest.