Preparation of templates for methylation analysis

1. A kit for use in preparing a sequencing library, the kit comprising adaptor polynucleotides, wherein:

each of the adaptor polynucleotides comprises a plurality of consecutive nucleotides, the plurality of consecutive nucleotides, wherein all cytosine bases in the adaptor polynucleotides are methylated and wherein each of the adaptor polynucleotides comprises a region of double stranded nucleic acids and at least one region of single stranded nucleic acids, the region of single-stranded nucleic acids forming a forked end; and

the plurality of consecutive nucleotides is complementary to the last 21 consecutive nucleotides of SEQ ID NO: 6.

2. The kit of claim 1 , wherein the at least one region of single stranded nucleic acids comprises the plurality of consecutive nucleotides.

3. The kit of claim 1 , wherein the region of double stranded nucleic acids comprises 5 or more consecutive base pairs.

4. The kit of claim 1 , wherein the adaptor polynucleotides are phosphorylated at a 5′ end of the region of double stranded nucleic acids.

5. The kit of claim 1 , wherein the kit comprises two or more amplification primers, at least one of the amplification primers comprising a region that hybridizes to the at least one region of single stranded nucleic acids.

6. The kit of claim 1 , wherein the kit comprises two or more amplification primers, at least one of the amplification primers comprising a region that extends beyond a 5′ end of the at least one region of single stranded nucleic acids.

7. The kit of claim 1 , wherein the kit comprises two or more amplification primers, at least one of the amplification primers comprising a region that hybridizes to, and extends beyond, a 5′ end of the at least one region of single stranded nucleic acids.

8. The kit of claim 1 , wherein the kit comprises first oligonucleotide primers configured to anneal to the adaptor polynucleotides and second oligonucleotide primers configured to anneal to a region of extended strands produced by extension of the first oligonucleotide primers.

9. The kit of claim 8 , wherein the first oligonucleotide primers and the second oligonucleotide primers are capable of annealing to one strand in the region of double stranded nucleic acids of the adaptor polynucleotides.

10. The kit of claim 9 , wherein the first oligonucleotide primers and the second oligonucleotide primers comprise one or more of SEQ ID NO: 3 and SEQ ID NO: 4.

11. The kit of claim 1 , wherein the adaptor polynucleotides comprise forked universal adaptors.

12. The kit of claim 1 , wherein the adaptor polynucleotides comprise universal adaptors.

13. The kit of claim 1 , further comprising oligonucleotide primers capable of annealing to the adaptor polynucleotides.

14. The kit of claim 13 , wherein the oligonucleotide primers are configured to anneal to at least one region of single stranded nucleic acids of the adaptor polynucleotides.

15. The kit of claim 1 , wherein the adaptor polynucleotides comprise one or more of SEQ ID NO: 1 and SEQ ID NO: 2.

16. A method of analysing methylation status of cytosine bases in a nucleic acid, comprising:

(a) providing a sample of double stranded nucleic acid target fragments derived from said nucleic acid;

(b) ligating universal adaptors to the double stranded nucleic acid target fragments to produce adaptor-ligated double stranded nucleic acid target fragments, wherein:

cytosine bases in the universal adaptors are methylated,

each of the universal adaptors comprises a plurality of consecutive nucleotides,

wherein each of the universal adaptors comprises a region of double stranded nucleic acids and at least one region of single stranded nucleic acids, the region of single-stranded nucleic acids forming a forked end, and

the plurality of consecutive nucleotides is complementary to nucleotides in the last 21 consecutive nucleotides of SEQ ID NO: 6;

(c) treating the adaptor-ligated double stranded nucleic acid target fragments with a reagent that converts non-methylated cytosine bases to uracil to produce a treated sample of adaptor-ligated double stranded nucleic acid target fragments;

(d) sequencing the treated adaptor-ligated double stranded nucleic acid target fragments; and

(e) analysing sequences of the treated sample to determine which cytosine bases were converted to uracil bases, thereby determining the methylation status of the nucleic acid.