Method of detecting a nucleotide change in nucleic acids

An assay for a biologically derived denatured DNA or RNA test substance, which has a known normal nucleotide sequence and a known possible mutation at at least one target nucleotide position in said sequence, which assay determines whether the test substance has said normal nucleotide sequence or said possible mutation, said assay comprising the steps of

• (a) annealing a target oligonucleotide probe of predetermined sequence to a first sequence of said test substance so that said target nucleotide position is aligned with a nucleotide in an end region of said target probe,
• (b) annealing an adjacent oligonucleotide probe of predetermined sequence to a second sequence of said test substance contiguous to said first sequence, so that the terminal nucleotide in said end region of said target probe and one end of said adjacent probe are directly adjacent to each other,
• (c) contacting said annealed target probe and adjacent probe with a linking agent under conditions such that the directly adjacent ends of said probes covalently bond to form a linked probe product unless there is nucleotide base pair mismatching between said target probe and said test substance at the target nucleotide position,
• (d) separating said test substance and linked probe product, if formed, and
• (e) detecting whether or not said linked probe product is formed as an indication of nucleotide base pair matching or mismatching at said target nucleotide position.