METHODS FOR DEPLETION OF HIGH-COPY SEQUENCES IN MULTIPLEXED WHOLE GENOME SEQUENCING LIBRARIES
A depleted sequencing library can be prepared by providing a composition comprising a heterogeneous mixture of linear nucleic acids having a first terminus and a second terminus. A first subset of target nucleic acids and a second subset of non-target nucleic acids can include a first adaptor region at the first terminus and a second adaptor region at the second terminus. A third subset of the target nucleic acids and a fourth subset of the non-target nucleic acids include the second adaptor region at the first terminus and at the second terminus. Removable blocker oligonucleotides can be added to the composition, non-target nucleic acids can be removed from the composition by sequence capture to bait oligonucleotides, and the composition can be treated to reduce a quantity of free blocker oligonucleotides that are not annealed to an adaptor sequence or to a sequence substantially complementary to an adaptor sequence.
1 . A method for preparing a depleted sequencing library comprising:
providing a composition comprising a heterogeneous mixture of linear nucleic acids having a first terminus and a second terminus, wherein the mixture comprises a plurality of target nucleic acids and a plurality of non-target nucleic acids, and wherein at least some of the nucleic acids comprise adaptor regions at one or both termini;
adding removable blocker oligonucleotides to the composition, wherein at least a portion of the removable blocker oligonucleotides are RNA oligonucleotides, and wherein the blocker oligonucleotides anneal to adaptor sequences in the composition;
removing non-target nucleic acids by hybridization to bait oligonucleotides; and
treating the composition to reduce the quantity of removable blocker oligonucleotides that are not annealed to an adaptor sequence.
2 . The method of claim 1 , wherein the treating step of treating the composition comprises using a combination of heat of at least 70° C., addition of divalent ions, and a pH greater than 7.
3 . The method of claim 2 , wherein the heat treatment is performed for at least 5 minutes.
4 . The method of claim 2 , wherein the divalent ion comprises magnesium or calcium.
5 . The method of claim 2 , wherein the pH is between 7.5 and 9.0.
6 . The method of claim 1 , wherein the removable blocker oligonucleotides are removed under the same conditions regardless of whether they are annealed or unannealed.
7 . The method of claim 1 , wherein the removable blocker oligonucleotides comprise both RNA and DNA oligonucleotides.
8 . The method of claim 7 , wherein the DNA oligonucleotides comprise uracil.
9 . The method of claim 8 , wherein the DNA oligonucleotides are degraded by a uracil-DNA-glycosylase.
10 . The method of claim 1 , wherein the removable blocker oligonucleotides are between 40 and 80 nucleotides in length.
11 . The method of claim 1 , wherein the removable blocker oligonucleotides are added in an amount sufficient to exceed the molar concentration of adaptor sequences.
12 . The method of claim 1 , wherein the treating comprises enzymatic degradation of the RNA oligonucleotides.
13 . The method of claim 12 , wherein the enzyme is an RNase.
14 . The method of claim 1 , wherein the treating comprises physical separation using solid-phase extraction.
15 . The method of claim 1 , wherein the bait oligonucleotides comprise an affinity label.
16 . The method of claim 15 , wherein the affinity label is biotin.
17 . The method of claim 1 , wherein the bait oligonucleotides are complementary to repetitive sequences or transposable elements.
18 . The method of claim 1 , wherein the composition comprises nucleic acids derived from multiple biological samples.
19 . The method of claim 18 , wherein the nucleic acids from each biological sample comprise a sample-specific barcode sequence.
20 . The method of claim 1 , further comprising sequencing at least a portion of the target nucleic acids.