Method for the particularly sensitive detection of nucleic acids

DETAILED DESCRIPTION We claim: 1.
A method of detecting a target nucleic acid A, comprising: a) hybridizing the target nucleic acid A with a probe nucleic acid B comprising (1) a sequence B1 which base pairs with at least a part of the target nucleic acid A, and (2) a sequence B2, to produce a first hybrid, b) cleaving the hybridized probe nucleic acid B to produce a cleavage product B' comprising the sequence B2, c) hybridizing the cleavage product B' with a template nucleic acid C comprising (1) a sequence C2 which base pairs with at least a part of the cleavage product B', and (2) a sequence C1 which does not hybridize with the sequence B1 of the probe nucleic acid B, to produce a second hybrid, d) extending the hybridized cleavage product B' with an extension sequence B3 which is template-specific to at least a part of the sequence C1, to produce a first extension product, e) hybridizing a probe D with the first extension product to produce a third hybrid, wherein the probe D comprises (1) a sequence D1 which base pairs with the extension sequence B3, and (2) a sequence D2, and detecting the products formed in at least one of the steps b), d) and e).
2.
The method as claimed in claim 1, further comprising, between step e) and said detecting step, f) cleaving the probe D of the third hybrid formed in step e) to produce digestion products comprising the first extension product and a cleavage product D' comprising the sequence D2, and wherein said detecting step comprises detecting the products formed in at least one of the steps b), d), e) and f).
3.
The method as claimed in claim 2, further comprising, between step f) and said detecting step, g) hybridizing the cleavage product D' with a template nucleic acid E comprising (1) a sequence E2 which base pairs with at least a part of the cleavage product D', and (2) a sequence El which does not hybridize with the sequence D1 of the probe D, and h) extending the cleavage product D' with an extension sequence D3 which is template-specific to at least a part of the sequence E1, to produce a second extension product, and wherein said detecting step comprises detecting the products formed in at least one of the steps b), d), e), f), and h)