RECOGNITION OF DOUBLE-STRANDED DNA BY PEPTIDE NUCLEIC-ACID

Peptide nucleic acid (PNA) is an oligonucleotide mimic in which the ba ckbone of DNA has been replaced by a pseudopeptide. We here show that there are distinct variations as to how PNA oligomers interact with do uble-stranded DNA depending on choice of nucleobases. Thymine-rich hom opyrimidine PNA oligomers recognise double-stranded polynucleotides by forming PNA(2)-DNA triplexes with the DNA purine strand. By contrast, cytosine-rich homopyrimidine PNAs add to double-stranded polynucleoti des as Hoogsteen strands, forming PNA-DNA(2) triplexes, while homopuri ne, or alternating thymine-guanine, PNA oligomers invade DNA to form P NA-DNA duplexes.