Compositions and methods for polynucleotide sequencing
Methods and compositions for characterizing a target polynucleotide, including, characterizing the sequence of the target polynucleotide, using the fractional translocation steps of the target polynucleotide's translocation through a pore.
1. A method of characterizing a target polynucleotide, the method comprising:
(a) applying a potential difference across a pore in contact with a Hel308 helicase and the target polynucleotide;
(b) measuring at least two electrical signals for a unit of one or more nucleotides of the target polynucleotide moving through the pore during a full translocation cycle of the Hel308 helicase;
(c) characterizing the target polynucleotide using the at least two electrical signals measured in (b); and
wherein the unit of one or more nucleotides of the target polynucleotide passing through the pore during a full translocation cycle of the Hel308 helicase is characterized with an accuracy greater than 50% using the at least electrical two signals measured in (b), compared to characterization of the unit of one or more nucleotides of the target polynucleotide using a single electrical signal measured during the full translocation cycle.
2. The method of claim 1 , wherein characterizing the target polynucleotide comprises identifying one or more characteristics selected from the group consisting of a sequence of the target polynucleotide, a modification of the target polynucleotide, a length of the target polynucleotide, an identity of the target polynucleotide, a source of the target polynucleotide, and a secondary structure of the target polynucleotide.
3. The method of claim 1 , wherein the potential difference comprises an electric potential difference.
4. The method of claim 2 or 3 , further comprising repeating steps (a)-(c) one or more times.
5. The method of claim 1 , wherein a translocation of the target polynucleotide is in a direction opposite of the applied force applied by the potential difference on the polynucleotide translocating through the pore.
6. The method of claim 1 , wherein a translocation of the target polynucleotide is in a direction with the applied force applied by the potential difference on the polynucleotide translocating through the pore.
7. The method of claim 1 , wherein the pore is a biological pore.
8. The method of claim 7 , wherein the biological pore comprises a Mycobacterium smegmatis porin A (MspA).
9. The method of claim 8 , wherein the MspA has an amino acid sequence of SEQ ID NO: 1 or having at least 99% homology to SEQ ID NO: 1.
10. The method of claim 1 , wherein the pore is a solid state pore.
11. The method of claim 1 , wherein the pore is a biological and solid state hybrid pore.
12. The method of claim 1 , wherein the Hel308 helicase is a helicase shown in Tables 1 and 2.
13. The method of claim 1 , wherein the characterizing comprises applying a modified Viterbi algorithm.
14. The method of claim 1 , further comprising:
(d) after step (c), varying at least one parameter so as to vary a timing of one or more fractional translocation steps by said Hel308 helicase of said target polynucleotide through the pore; and
(e) repeating steps (a)-(c) using the varied at least one parameter.
15. The method of claim 14 , further comprising combining the signals produced during steps (c) and (e) and characterizing the target polynucleotide based on the combined signals.
16. The method of claim 15 , wherein the varied at least one parameter is selected from the group consisting of temperature, salt concentration, cofactor concentration, concentration of ATP product, pH, and the particular Hel308 helicase used.
17. The method of claim 1 , wherein the characterizing comprises detecting and identifying levels in at least two electrical signals and determining and outputting a sequence of the target polynucleotide based on the detected and identified levels.