Allele-specific sequence variation analysis
Fragmentation-based methods and systems, particularly mass spectrometry based methods and systems, for the analysis of sequence variations including haplotypes are provided. Also provided are methods for obtaining a specific allele from a nucleic acid mixture, such as genomic DNA.
1. A method for haplotyping a plurality of polymorphic markers, comprising:
a) amplifying a target DNA molecule, using two primers, wherein one of the primers is allele-specific, and wherein at least one of the primers comprises an RNA promoter in the presence of
i. a competitor oligonucleotide comprising a modified 3′-end nucleotide selected from an inverted base, a dideoxynucleotide bound to the penultimate nucleotide by a methylphosphonate link, a ribonucleotide, a 3′ Phosphate, a carbon chain spacer, or a peptide nucleic acid (PNA), wherein the competitor is an extension inhibitor of an unwanted allele, and
ii. a mixture of thermostable DNA polymerases, wherein at least one of the polymerases comprises 3′-5′ exonuclease activity, and
obtaining a double stranded DNA molecule;
b) fragmenting the double stranded DNA molecule, or an RNA product transcribed from the double stranded DNA molecule, at a plurality of specific and predictable sites;
c) fragmenting or simulating fragmentation of a reference nucleic acid into fragments at the same plurality of specific and predictable sites of step b);
d) comparing the fragments of step b) with the fragments or simulated fragments of step c); and
e) from the comparison of fragments of d), haplotyping a plurality of linked SNPs on the target DNA molecule corresponding to a single or specific allele at one or more loci, in a single reaction.
2. The method of claim 1 , comprising detecting a previously undiscovered SNP within the haplotype.
3. The method of claim 1 , comprising haplotyping three or more linked SNPs on the target DNA molecule.
4. The method of claim 1 , comprising haplotyping four or more linked SNPs on the target molecule.
5. The method of claim 1 , comprising haplotyping two or more linked SNPs on the same gene.
6. The method of claim 1 , comprising haplotyping three or more linked SNPs on the same gene.
7. The method of claim 1 , wherein the target DNA is not amplified before step a).
8. The method of claim 1 , wherein the amplification step is PCR amplification from a diluted DNA sample containing an amount of haploid genome equivalents selected from 10, 9, 8, 7, 6, 5, 4, 3, 2 or 1.
9. The method of claim 1 , wherein the competitor oligonucleotide is added to the amplification reaction in an excess amount over a concentration of an Allele-Specific PCR amplification primer selected from among: 1-fold, 2-fold, 3-fold, 4-fold, 5-fold, 10-fold, 15-fold, 20-fold, 25-fold, 30-fold, 35-fold, 40-fold, 45-fold, 50-fold, 55-fold, 60-fold, 65-fold, 70-fold or 75-fold or more.
10. The method of claim 1 , wherein the target DNA molecule corresponding to a single or specific allele is present in less than 10% of the nucleic acid present in a sample mixture.
11. The method of claim 1 , wherein the target DNA molecule corresponding to a single or specific allele is present in less than 5% of the nucleic acid present in a sample mixture.
12. The method of claim 1 , wherein both oligonucleotide primers comprise RNA promoter sequences.
13. The method of claim 1 , wherein the haplotyping step comprises:
f) determining mass signals of the fragments produced in b) and c);
g) determining differences in the mass signals between the fragments produced in a) and the fragments produced in b); and
h) determining a reduced set of sequence variation candidates from the differences in the mass signals and thereby determining sequence variations in the target DNA molecule compared to the reference nucleic acid.
14. The method of claim 13 , wherein determining sequence variations comprises:
i) identifying fragments that are different between the target DNA molecule and the reference nucleic acid;
j) determining compomers corresponding to the identified different fragments in step h) that are compomer witnesses; and
k) determining a reduced set of sequence variations corresponding to the compomer witnesses that are candidate sequences to determine the sequence variations in the target DNA molecule compared to the reference nucleic acid.
15. The method of claim 1 , wherein the haplotyping step comprises mass spectrometric analysis.
16. The method of claim 1 , wherein the mixture of thermostable DNA polymerases is selected from the group consisting of Taq/Pfu, Taq/Deep Vent, Taq/Vent, Taq/Pwo, Taq/Tgo, Klentaq1/Pfu, Klentaq1/Deep Vent, Klentaq1/Vent/Klentaq1/Pwo, and Klentaq1/Tgo.
17. The method of claim 1 , wherein the amplified double stranded DNA molecule is more than 1 kb.
18. The method of claim 1 , wherein the amplified double stranded DNA molecule is more than 2 kb.
19. The method of claim 1 , wherein the amplified double stranded DNA molecule is more than 5 kb.
20. The method of claim 1 , wherein the modified 3′-end nucleotide is an inverted base.
21. The method of claim 1 , wherein the modified 3′-end nucleotide is a ribonucleotide.
22. The method of claim 1 , wherein the modified 3′-end nucleotide is a 3′ Phosphate.
23. The method of claim 1 , wherein the modified 3′-end nucleotide is a carbon chain spacer.
24. The method of claim 1 , wherein the modified 3′-end nucleotide is a peptide nucleic acid (PNA).
25. The method of claim 23 , wherein the carbon chain spacer is selected from the group consisting of C-3, C-5, C-7, C-9 and C-12.
26. The method of claim 1 , wherein the modified 3′-end nucleotide is a dideoxynucleotide bound to the penultimate nucleotide by a methylphosphonate link.