Method for modifying a template double stranded polynucleotide using a MuA transposase

1. A method for modifying a template double stranded polynucleotide, comprising:

(a) contacting the template polynucleotide with a MuA transposase and a population of double stranded MuA substrates each comprising (i) at least one overhang and (ii) at least one hairpin loop in the opposite strand from the strand comprising the at least one overhang such that the transposase fragments the template polynucleotide and ligates a substrate to one or both ends of the double stranded fragments and thereby produces a plurality of fragment/substrate constructs;

(b) contacting the fragment/substrate constructs with a polymerase such that the polymerase displaces the strands comprising the overhangs and replaces them with strands which complement the strands comprising the hairpin loops and thereby produces a plurality of double stranded constructs each comprising a double stranded fragment of the template polynucleotide; and

(c) separating the two strands of the double stranded constructs and using the strands as templates to form a plurality of modified double stranded polynucleotides each comprising two complementary strands linked by at least one hairpin loop.

2. A method according to claim 1 , wherein step (c) comprises separating the two strands of the double stranded constructs by increasing one or more of pH, temperature and ionic strength.

3. A method according to claim 1 , wherein step (c) comprises contacting the separated strands with a polymerase such that the polymerase uses the strands as templates to form the plurality of modified double stranded polynucleotides.

4. A method according to claim 1 , wherein step (c) comprises (i) contacting the plurality of separated strands with a population of nucleotide oligomers which comprises every possible combination of nucleotides which are complementary to all of the nucleotides in the strands under conditions in which the oligomers are capable of hybridising to the strands and (ii) ligating together those oligomers that hybridise to the strands to form the plurality of modified double stranded polynucleotides.

5. A method according to claim 1 , wherein step (c) comprises contacting the plurality of double stranded constructs with a polymerase such that the polymerase simultaneously separates the two strands of the double stranded constructs and uses the strands as templates to form the plurality of modified double stranded polynucleotides.

6. A method according to claim 1 , wherein the at least one hairpin loop does not link the two strands of each substrate.

7. A method according to claim 1 , wherein the at least one overhang is 4, 5 or 6 nucleotides in length.

8. A method according to claim 1 , wherein each substrate comprises a selectable binding moiety.

9. A method according to claim 1 , wherein each substrate comprises a leader sequence which is capable of threading through a transmembrane pore.

10. A method according to claim 1 , wherein the method further comprises (d) attaching Y adaptors to the plurality of modified double stranded polynucleotides at the opposite ends from the hairpin loops and wherein the Y adaptors optionally comprise a leader sequence which is capable of threading through a transmembrane pore.

11. A method according to claim 1 , wherein the method further comprises binding one or more polynucleotide binding proteins to the plurality of modified double stranded polynucleotides.

12. A method of characterising at least one polynucleotide modified using a method according to claim 1 , comprising:

a) contacting the modified polynucleotide with a transmembrane pore such that at least one strand of the polynucleotide moves through the pore; and

b) taking one or more measurements as the at least one strand moves with respect to the pore wherein the measurements are indicative of one or more characteristics of the at least one strand and thereby characterising the modified polynucleotide.

13. A method of characterising a template polynucleotide, comprising:

a) modifying the template polynucleotide using a method according to claim 1 to produce a plurality of modified polynucleotides;

b) contacting each modified polynucleotide with a transmembrane pore such that at least one strand of each polynucleotide moves through the pore; and

c) taking one or more measurements as each polynucleotide moves with respect to the pore wherein the measurements are indicative of one or more characteristics of each polynucleotide and thereby characterising the template polynucleotide.

14. A method according to claim 12 , wherein both strands of the/each modified polynucleotide move through the pore.

15. A method according to claim 12 , wherein the one or more characteristics are selected from (i) the length of the polynucleotide, (ii) the identity of the polynucleotide, (iii) the sequence of the polynucleotide, (iv) the secondary structure of the polynucleotide and (v) whether or not the polynucleotide is modified.

16. A method according to claim 12 , wherein contacting step (a) or contacting step (b) further comprises contacting the/each modified polynucleotide with a polynucleotide binding protein such that the protein controls the movement of the/each polynucleotide through the pore.

17. A method according to claim 16 , wherein the method comprises

(i) contacting the/each modified polynucleotide with a transmembrane pore and one or more polynucleotide binding proteins such that at least one strand of the/each polynucleotide moves through the pore and the one or more proteins control the movement of the/each polynucleotide through the pore; and

(ii) measuring the current passing through the pore as the/each polynucleotide moves with respect to the pore wherein the current is indicative of one or more characteristics of the/each polynucleotide and thereby characterising the polynucleotide.

18. A method according to claim 17 , wherein the one or more polynucleotide binding proteins are bound to the/each modified polynucleotide before it is/they are contacted with the transmembrane pore.

19. A method according to claim 17 , wherein the one or more polynucleotide binding proteins are one or more helicases.