Enzyme method

1. A method of characterising a target polynucleotide, comprising:

(a) contacting the target polynucleotide with a transmembrane pore under an applied voltage field such that a portion of the target polynucleotide is captured by the transmembrane pore, wherein the pore is present in a membrane;

(b) contacting the target polynucleotide with a Hel308 helicase on the cis side of the membrane such that the helicase binds to the target polynucleotide, thereby controlling the movement of the target polynucleotide through the transmembrane pore against the applied voltage field from the trans side of the membrane to the cis side of the membrane; and

(c) measuring one or more characteristics of the target polynucleotide as the target polynucleotide moves through the transmembrane pore, thereby characterising the target polynucleotide.

2. The method according to claim 1 , wherein the one or more characteristics are selected from (i) the length of the target polynucleotide, (ii) the identity of the target polynucleotide, (iii) the sequence of the target polynucleotide, (iv) the secondary structure of the target polynucleotide and (v) whether or not the target polynucleotide is modified.

3. The method according to claim 2 , wherein the target polynucleotide is modified by methylation, by oxidation, by damage, with one or more proteins, or with one or more labels, tags, or spacers.

4. The method according to claim 1 , wherein at least a portion of the target polynucleotide is double stranded.

5. The method according to claim 1 , wherein the transmembrane pore is a protein pore.

6. The method according to claim 5 , wherein the transmembrane protein pore is selected from the group consisting of: .alpha.-hemolysin, leukocidin, Mycobacterium smegmatis porin A (MspA), outer membrane porin F (OmpF), outer membrane porin G (OmpG), outer membrane phospholipase A, Neisseria autotransporter lipoprotein (NalP) and WZA.

7. The method according to claim 1 , wherein the Hel308 helicase comprises the amino acid motif Q-X 1 -X 2 -G-R-A-G-R (SEQ ID NO: 8), wherein X 1 is C, M or L and X 2 is any amino acid residue.

8. The method according to claim 7 , wherein X 2 is A, F, M, C, V, L, I, S, T or P.

9. The method according to claim 1 , wherein the Hel308 helicase binds to the target polynucleotide at an internal nucleotide.

10. The method according to claim 1 , wherein the one or more characteristics of the target polynucleotide are measured by electrical measurement and/or optical measurement.

11. The method according to claim 10 , wherein the electrical measurement is a current measurement, an impedance measurement, a tunnelling measurement, or a field effect transistor (FET) measurement.

12. The method according to claim 1 , wherein at least a portion of the polynucleotide is double stranded.

13. The method according to claim 1 , wherein, prior to the movement of the target polynucleotide through the transmembrane pore from the trans side of the membrane to the cis side of the membrane, the target polynucleotide moves from the cis side of the membrane to the trans side of the membrane.

14. The method according to claim 13 , wherein the portion of the target polynucleotide that is captured by a transmembrane pore is the 3′ end of the target polynucleotide.

15. The method according to claim 1 , wherein the portion of the target polynucleotide that is captured by a transmembrane pore is the 5′ end of the target polynucleotide.

16. The method according to claim 1 , wherein the target polynucleotide is partially translocated through the pore in (a).

17. The method according to claim 1 , wherein method is carried out using a salt concentration of at least 0.3 M or at least 1.0 M and the salt is optionally KCl.

18. The method according to claim 1 , wherein an initial helicase controls the movement of the target polynucleotide into the pore in (a).

19. The method according to claim 18 , wherein the Hel308 helicase of (a) binds to an internal polynucleotide of the target polynucleotide at a location on the polynucleotide different than the initial helicase.

20. The method according to claim 1 , wherein the transmembrane pore is a solid state pore.