SYSTEMS AND METHODS FOR SEQUENCING WITH MULTI-PRIMING
Provided herein are systems, methods, compositions, and kits for sequencing with multi-priming. In some cases, multiple distinct primer molecules may be provided to a template nucleic acid to hybridize to distinct regions of the template nucleic acid. In some cases, a connected primer molecule may be provided to a template nucleic acid to have multiple distinct primer regions hybridize to distinct regions of the template nucleic acid. Non-adjacent regions of the template nucleic acid may be sequenced in distinct sequencing operations.
1 - 144 . (canceled)
145 . A method, comprising:
(a) hybridizing a first primer region and a second primer region of a primer molecule to a first target region and a second target region, respectively, of a target nucleic acid strand, wherein an intermediary region is disposed between the first target region and the second target region on the target nucleic acid strand, wherein a connector region is disposed between the first primer region and the second primer region;
(b) extending the primer molecule from the second primer region to generate a first sequencing read for a first region of the target nucleic acid strand;
(c) cleaving the primer molecule to activate the first primer region for extension; and
(d) extending the primer molecule from the first primer region to generate a second sequencing read for a second region of the target nucleic acid strand, wherein the second region is different from the first region.
146 . The method of claim 145 , wherein the target nucleic acid strand is coupled to a support.
147 . The method of claim 146 , wherein the support is a bead, and wherein the bead is immobilized to an individually addressable location of a plurality of individually addressable locations on a substrate.
148 . The method of claim 147 , wherein the plurality of individually addressable locations comprises at least 1,000,000,000 individually addressable locations.
149 . The method of claim 145 , wherein the first target region is disposed 3′ to the second target region on the target nucleic acid strand.
150 . The method of claim 145 , wherein the first region or the second region comprises at least a portion of the intermediary region.
151 . The method of claim 145 , wherein the primer molecule comprises one or more cleavage sites disposed between the first primer region and the connector region.
152 . The method of claim 151 , wherein the one or more cleavage sites comprises one or more members selected from the group consisting of: uracil, ribonucleotide, inosine, FapyG, 8oxoG, C3 spacer, photocleavable moiety, azobenzene, and abasic site.
153 . The method of claim 152 , wherein the one or more cleavage sites comprises one or more uracils, and (c) comprises using a uracil-specific excision reagent (USER) enzyme to excise the one or more uracils.
154 . The method of claim 145 , further comprising, prior to (d), terminating extension of the second primer region in (b).
155 . The method of claim 154 , wherein the terminating occurs prior to (c).
156 . The method of claim 154 , wherein the terminating comprises incorporation of a terminated nucleotide.
157 . The method of claim 156 , wherein the second primer region is phosphorylated, and the terminating comprises using a phosphate-dependent enzyme to degrade the second primer region.
158 . The method of claim 145 , further comprising, prior to (d), degrading a first extension strand extended from the second primer region via an exonuclease.
159 . The method of claim 158 , wherein a 3′ end of the first primer region is protected, and the first extension strand is degraded using an Exonuclease III.
160 . The method of claim 145 , wherein the intermediary region comprises one or more of a barcode, a sample index, and a unique molecular identifier.
161 . The method of claim 145 , wherein the intermediary region comprises between 10 and 60 bases.
162 . The method of claim 145 , wherein the first target region or the second target region comprises a polyT homopolymer region.
163 . The method of claim 162 , wherein the first primer region or the second primer region comprises a polyA sequence of at least 10 bases in length.
164 . The method of claim 145 , further comprising associating the first sequencing read and the second sequencing read via a respective individually addressable location of sequencing signals detected on a substrate during generation of the first sequencing read and the second sequencing read.