Methods for sequencing a biomolecule by detecting relative positions of hybridized probes
A sequencing method is presented in which a biomolecule is hybridized with a specially chosen pool of different probes of known sequence which can be electrically distinguished. The different probe types are tagged such that they can be distinguished from each other in a Hybridization Assisted Nanopore Sequencing (HANS) detection system, and their relative positions on the biomolecule can be determined as the biomolecule passes through a pore or channel. The methods eliminate, resolve, or greatly reduce ambiguities encountered in previous sequencing methods.
1. A method for determining a sequence of a biomolecule, the method comprising the steps of:
(a) identifying a set of k−1-length subsequences that represent a plurality of substrings of a sequence string s of the biomolecule;
(b) for each of the k−1-length subsequences, forming a pool of probes comprising four different k-mer extensions of the k−1-length subsequence;
(c) for each pool formed in step (b):
(i) hybridizing the biomolecule with the four k-mer probes making up the pool; and
(ii) detecting relative positions of the k-mer probes that have attached to the biomolecule; and
(d) ordering the subsequences corresponding to the detected attached probes to determine the sequence string s of the biomolecule.
2. The method of claim 1 , wherein each of the four k-mer probes in step (c) has a distinguishable tag attached, such that there are four different detectable tags used for a given pool of k-mers.
3. The method of claim 2 , wherein step (c)(i) comprises hybridizing the biomolecule with all four of the k-mer probes making up the pool prior to detecting the relative positions of the attached k-mer probes in step (c)(ii), such that step (c)(ii) results in detecting the relative positions of all four of the k-mer probes making up the pool.
4. The method of claim 1 , wherein step (c) comprises:
(A) hybridizing the biomolecule with two different k-mer probes selected from the four k-mer probes making up the pool, wherein the two selected k-mer probes have tags attached that are distinguishable from each other;
(B) following (A), where one or more binding events occur involving both of the selected k-mer probes, detecting relative positions of the two different k-mer probes that have attached to the biomolecule; and
(C) repeating (A) and (B) with another two different k-mer probes selected from the four k-mer probes making up the pool until hybridizations and detections are performed for all six pair combinations of the four k-mer probes making up the pool, thereby detecting the relative positions of all four of the k-mer probes making up the pool.
5. The method of claim 1 , wherein step (c) comprises:
(A) hybridizing the biomolecule with a set of three k-mer probes selected from the four k-mer probes making up the pool, wherein the three selected k-mer probes have tags attached that are distinguishable from each other;
(B) following (A), where one or more binding events occur involving two or three of the selected k-mer probes, detecting relative positions of the two or three k-mer probes that have attached to the biomolecule; and
(C) repeating (A) and (B) with a different set of three k-mer probes selected from the four k-mer probes making up the pool until hybridizations and detections are performed for all four three-member combinations of the four k-mer probes making up the pool, thereby detecting the relative positions of all four of the k-mer probes making up the pool.
6. The method of claim 1 , wherein step (c)(ii) comprises using HANS to detect the relative positions of the k-mer probes.
7. The method of claim 6 , wherein step (c)(ii) comprises monitoring an electrical signal across a fluidic channel or pore or within a fluidic volume of a channel or pore as the hybridized biomolecule translocates therethrough, the electrical signal being indicative of hybridized portions of the biomolecule and non-hybridized portions of the biomolecule.
8. The method of claim 7 , wherein the detected electrical signal allows differentiation between at least two of the k-mer probes hybridized to the biomolecule.
9. The method of claim 1 , wherein step (c)(ii) comprises detecting an optical signal indicative of the relative position of at least two of the k-mer probes hybridized to the biomolecule.
10. The method of claim 1 , wherein the set of k−1-length subsequences represents all possible substrings of length k−1 in the sequence string s.
11. The method of claim 1 , wherein k is an integer from 3 to 10.
12. The method of claim 1 , wherein s is a sequence string at least 100 bp in length.