Self-folding amplification of target nucleic acid

1. A method for selective amplification of a target polynucleotide sequence (T), comprising the steps of:

(a) hybridizing the target polynucleotide sequence (+) with a first composite primer (−), said first composite primer comprising a 5′ promoter portion (P) and a 3′ target-recognition portion which is complementary to the 3′ end portion of the target polynucleotide sequence, wherein the first composite primer comprises a first self-folding segment between the promoter portion and the 3′ target recognition region;

(b) identifying the 5′ end portion of the target polynucleotide sequence;

(c) extending the 3′ end of the first composite primer and generating a first single-stranded DNA template (−) comprising the promoter portion (P) and the complementary sequence of the target polynucleotide sequence (Tc), said first single-stranded DNA template comprising the first self-folding segment and a second self-folding segment that is complementary to the first self-folding segment, wherein the promoter portion (P) is at the 5′ end of the first single-stranded DNA template and the second self-folding segments is at the 3′ end of the first single-stranded DNA template;

(d) allowing the first single-stranded DNA template to self-fold and form a first handle-stem-loop structure, which comprises a 5′ single-stranded handle comprising the promoter portion (P) and a double-stranded stem comprising the first and second self-folding segments hybridized to each other;

(e) extending the 3′ end of the first handle-stem-loop structure to generate a double-stranded promoter comprising the promoter portion (P) and its complementary sequence (Pc) hybridized to each other; and

(f) initiating transcription from the double-stranded promoter to generate multiple copies of a single-stranded RNA product (+) comprising the target polynucleotide sequence (T).

2. The method of claim 1 , wherein the target polynucleotide sequence is RNA.

3. The method of claim 2 , wherein step (c) comprises extending the 3′ end of the first composite primer to generate a first RNA/DNA hybrid and removing the RNA portion of the first RNA/DNA hybrid to generate the first single-stranded DNA template.

4. The method of claim 3 , wherein the target polynucleotide sequence is within a longer polynucleotide template, and wherein step (b) comprises identifying the 5′ end of the target polynucleotide sequence by using an enzyme to cleave at a region of the polynucleotide template immediately upstream of the 5′ end of the target polynucleotide sequence.

5. The method of claim 3 , wherein the target polynucleotide sequence is within a longer polynucleotide template, and wherein step (b) comprises identifying the 5′ end of the target polynucleotide sequence by hybridizing a blocking oligonucleotide (−) to a region of the polynucleotide template immediately upstream of the 5′ end of the target polynucleotide sequence, wherein said blocking oligonucleotide block extension of the first composite primer in step (c).

6. The method of claim 5 , wherein the first composite primer further comprises, between the promoter portion (P) and the 3′ target-recognition portion, a segment corresponding to the 5′ end portion of the target polynucleotide sequence, wherein this segment and its complementary sequence form said first pair of self-folding segments, the method further comprising the following steps after step (f):

(g) hybridizing the single-stranded RNA product (+) with the first composite primer (−) and extending the 3′ end of the first composite primer to generate a second RNA/DNA hybrid;

(h) removing the RNA portion of the second RNA/DNA hybrid to generate the first single-stranded DNA template (−); and

continuing steps (d), (e) and (f).

7. The method of claim 5 , wherein the 3′ target-recognition portion of the first composite primer comprises a segment corresponding to the 5′ end portion of the target polynucleotide sequence, wherein this segment and its complementary sequence form said first pair of self-folding segments, the method further comprising the following steps after step (f):

(g) hybridizing the single-stranded RNA product (+) with the first composite primer (−) and extending the 3′ end of the first composite primer to generate a second RNA/DNA hybrid;

(h) removing the RNA portion of the second RNA/DNA hybrid to generate a second single-stranded DNA template (−) comprising the promoter portion (P) and the complementary sequence of the target polynucleotide sequence (Tc), said second single-stranded DNA template comprising a second pair of self-folding segments that are complementary to each other, wherein the promoter portion (P) is at the 5′ end of the second single-stranded DNA template and one of the second pair of self-folding segments is at the 3′ end of the second single-stranded DNA template;

(i) allowing the second single-stranded DNA template to self-fold and form a second handle-stem-loop structure, which comprises a 5′ single-stranded handle comprising the promoter portion (P) and a double-stranded stem comprising the second pair of self-folding segments hybridized to each other;

(j) extending the 3′ end of the second handle-stem-loop structure to generate a double-stranded promoter comprising the promoter portion (P) and its complementary sequence (Pc) hybridized to each other; and

(k) initiating transcription from the double-stranded promoter to generate multiple copies of the single-stranded RNA product (+).

8. The method of claim 5 , wherein said first pair of self-folding segments comprise a segment corresponding to the 5′ end portion of the target polynucleotide sequence and its complementary sequence located at a separate portion of the target polynucleotide sequence, the method further comprising the following steps after step (f):

(g) hybridizing the single-stranded RNA product (+) with the first composite primer (−) and extending the 3′ end of the first composite primer to generate a second RNA/DNA hybrid;

(h) removing the RNA portion of the second RNA/DNA hybrid to generate a second single-stranded DNA template (−) comprising the promoter portion (P) and the complementary sequence of the target polynucleotide sequence (Tc), said second single-stranded DNA template comprising a second pair of self-folding segments that are complementary to each other, wherein the promoter portion (P) is at the 5′ end of the second single-stranded DNA template and one of the second pair of self-folding segments is at the 3′ end of the second single-stranded DNA template;

(i) allowing the second single-stranded DNA template to self-fold and form a second handle-stem-loop structure, which comprises a 5′ single-stranded handle comprising the promoter portion (P) and a double-stranded stem comprising the second pair of self-folding segments hybridized to each other;

(j) extending the 3′ end of the second handle-stem-loop structure to generate a double-stranded promoter comprising the promoter portion (P) and its complementary sequence (Pc) hybridized to each other; and

(k) initiating transcription from the double-stranded promoter to generate multiple copies of the single-stranded RNA product (+).

9. The method of claim 3 , wherein the target polynucleotide sequence is within a longer polynucleotide template, and wherein step (b) comprises identifying the 5′ end of the target polynucleotide sequence by hybridizing a template switching oligonucleotide (TSO) (−) to a region of the polynucleotide template immediately upstream of the 5′ end of the target polynucleotide sequence, and wherein step (c) comprises extending the 3′ end of the first composite primer over a portion of said template switching oligonucleotide (TSO).

10. The method of claim 9 , wherein the first composite primer further comprises, from 5′ to 3′ and between the promoter portion (P) and the 3′ target-recognition portion, a universal portion (U) that is not present in the target polynucleotide sequence or its complementary sequence, and the template switching oligonucleotide (TSO) comprising, from 5′ to 3′, the universal portion (U) and a portion complementary to the region of the polynucleotide template immediately upstream of the 5′ end of the target polynucleotide sequence, wherein the first pair of self-folding segments comprise the universal portion (U) and its complementary sequence, the method further comprising the following steps after step (f):

(g) hybridizing the single-stranded RNA product (+) with the first composite primer or a second composite primer (−) and extending the 3′ end of the second composite primer to generate a second RNA/DNA hybrid, wherein the second composite primer comprises the 5′ promoter portion (P) and the universal portion (U);

(h) removing the RNA portion of the second RNA/DNA hybrid to generate the first single-stranded DNA template (−); and

continuing steps (d), (e) and (f).

11. The method of claim 1 , wherein the target polynucleotide sequence is DNA.

12. The method of claim 11 , comprising a denaturing step before step (a).

13. The method of claim 12 , wherein the target polynucleotide sequence is within a longer polynucleotide template, and wherein step (b) comprises identifying the 5′ end of the target polynucleotide sequence by using an enzyme to cleave at a region of the polynucleotide template immediately upstream of the 5′ end of the target polynucleotide sequence.

14. The method of claim 12 , wherein the target polynucleotide sequence is within a longer polynucleotide template, and wherein step (b) comprises identifying the 5′ end of the target polynucleotide sequence by hybridizing a blocking oligonucleotide (−) to a region of the polynucleotide template immediately upstream of the 5′ end of the target polynucleotide sequence, wherein said blocking oligonucleotide block extension of the first composite primer in step (c).

15. The method of claim 14 , wherein the first composite primer further comprises, between the promoter portion (P) and the 3′ target-recognition portion, a segment corresponding to the 5′ end portion of the target polynucleotide sequence, wherein this segment and its complementary sequence form said first pair of self-folding segments, the method further comprising the following steps after step (f):

(g) hybridizing the single-stranded RNA product (+) with the first composite primer (−) and extending the 3′ end of the first composite primer to generate a RNA/DNA hybrid;

(h) removing the RNA portion of the RNA/DNA hybrid to generate the first single-stranded DNA template (−); and

continuing steps (d), (e) and (f).

16. The method of claim 14 , wherein the 3′ target-recognition portion of the first composite primer comprises a segment corresponding to the 5′ end portion of the target polynucleotide sequence, wherein this segment and its complementary sequence form said first pair of self-folding segments, the method further comprising the following steps after step (f):

(g) hybridizing the single-stranded RNA product (+) with the first composite primer (−) and extending the 3′ end of the first composite primer to generate a RNA/DNA hybrid;

(h) removing the RNA portion of the RNA/DNA hybrid to generate a second single-stranded DNA template (−) comprising the promoter portion (P) and the complementary sequence of the target polynucleotide sequence (Tc), said second single-stranded DNA template comprising a second pair of self-folding segments that are complementary to each other, wherein the promoter portion (P) is at the 5′ end of the second single-stranded DNA template and one of the second pair of self-folding segments is at the 3′ end of the second single-stranded DNA template;

(i) allowing the second single-stranded DNA template to self-fold and form a second handle-stem-loop structure, which comprises a 5′ single-stranded handle comprising the promoter portion (P) and a double-stranded stem comprising the second pair of self-folding segments hybridized to each other;

(j) extending the 3′ end of the second handle-stem-loop structure to generate a double-stranded promoter comprising the promoter portion (P) and its complementary sequence (Pc) hybridized to each other; and

(k) initiating transcription from the double-stranded promoter to generate multiple copies of the single-stranded RNA product (+).

17. The method of claim 14 , wherein said first pair of self-folding segments comprise a segment corresponding to the 5′ end portion of the target polynucleotide sequence and its complementary sequence located at a separate portion of the target polynucleotide sequence, the method further comprising the following steps after step (f):

(g) hybridizing the single-stranded RNA product (+) with the first composite primer (−) and extending the 3′ end of the first composite primer to generate a RNA/DNA hybrid;

(h) removing the RNA portion of the RNA/DNA hybrid to generate a second single-stranded DNA template (−) comprising the promoter portion (P) and the complementary sequence of the target polynucleotide sequence (Tc), said second single-stranded DNA template comprising a second pair of self-folding segments that are complementary to each other, wherein the promoter portion (P) is at the 5′ end of the second single-stranded DNA template and one of the second pair of self-folding segments is at the 3′ end of the second single-stranded DNA template;

(i) allowing the second single-stranded DNA template to self-fold and form a second handle-stem-loop structure, which comprises a 5′ single-stranded handle comprising the promoter portion (P) and a double-stranded stem comprising the second pair of self-folding segments hybridized to each other;

(j) extending the 3′ end of the second handle-stem-loop structure to generate a double-stranded promoter comprising the promoter portion (P) and its complementary sequence (Pc) hybridized to each other; and

(k) initiating transcription from the double-stranded promoter to generate multiple copies of the single-stranded RNA product (+).

18. The method of claim 12 , wherein the target polynucleotide sequence is within a longer polynucleotide template, and wherein step (b) comprises identifying the 5′ end of the target polynucleotide sequence by hybridizing a template switching oligonucleotide (TSO) (−) to a region of the polynucleotide template immediately upstream of the 5′ end of the target polynucleotide sequence, and wherein step (c) comprises extending the 3′ end of the first composite primer over a portion of said template switching oligonucleotide (TSO).

19. The method of claim 18 , wherein the first composite primer further comprises, from 5′ to 3′ and between the promoter portion (P) and the 3′ target-recognition portion, a universal portion (U) that is not present in the target polynucleotide sequence or its complementary sequence, and the template switching oligonucleotide (TSO) comprising, from 5′ to 3′, the universal portion (U) and a portion complementary to the region of the polynucleotide template immediately upstream of the 5′ end of the target polynucleotide sequence, wherein the first pair of self-folding segments comprise the universal portion (U) and its complementary sequence, the method further comprising the following steps after step (f):

(g) hybridizing the single-stranded RNA product (+) with the first composite primer or a second composite primer (−) and extending the 3′ end of the second composite primer to generate a second RNA/DNA hybrid, wherein the second composite primer comprises the 5′ promoter portion (P) and the universal portion (U);

(h) removing the RNA portion of the second RNA/DNA hybrid to generate the first single-stranded DNA template (−); and

continuing steps (d), (e) and (f).

20. The method of claim 1 , wherein the first composite primer further comprises, from 5′ to 3′ and between the promoter portion (P) and the 3′ target-recognition portion, a universal portion (U) that is not present in the target polynucleotide sequence or its complementary sequence, and a segment corresponding to the 5′ end portion of the target polynucleotide sequence, wherein this segment and its complementary sequence form said first pair of self-folding segments, the method further comprising the following steps after step (f):

(g) hybridizing the single-stranded RNA product (+) with the first composite primer or a second composite primer (−) and extending the 3′ end of the second composite primer to generate a second RNA/DNA hybrid, wherein the second composite primer comprises the 5′ promoter portion (P) and the universal portion (U);

(h) removing the RNA portion of the second RNA/DNA hybrid to generate a second single-stranded DNA template (−) comprising the promoter portion (P), the universal portion (U), and the complementary sequence of the target polynucleotide sequence (Tc), said second single-stranded DNA template comprises a second pair of self-folding segments that are complementary to and separated from each other, wherein the promoter portion (P) is at the 5′ end of the second single-stranded DNA template and one of the second pair of self-folding segments is at the 3′ end of the second single-stranded DNA template;

(i) allowing the second single-stranded DNA template to self-fold and form a second handle-stem-loop structure which comprises a 5′ single-stranded handle comprising the promoter portion (P), a double-stranded stem comprising the second pair of self-folding segments hybridized to each other, and a single-stranded loop comprising the sequence between the second pair of self-folding segments;

(j) extending the 3′ end of the second handle-stem-loop structure to generate a double-stranded promoter comprising the promoter portion (P) and its complementary sequence (Pc) hybridized to each other; and

(k) initiating transcription from the double-stranded promoter to generate multiple copies of the single-stranded RNA product (+).