TRIPLEX DNA STRUCTURES

A DNA tripler is formed when pyrimidine or purine bases occupy the maj or groove of the DNA double Helix forming Hoogsteen pairs with purines of the Watson-Crick basepairs. Intermolecular triplexes are formed be tween tripler forming oligonucleotides (TFO) and target sequences on d uplex DNA. Intramolecular triplexes are the major elements of H-DNAs, unusual DNA structures, which are formed in homopurine-homopyrimidine regions of supercoiled DNAs. TFOs are promising gene-drugs, which can be used in an anti-gene strategy, that attempt to modulate gene activi ty in vivo. Numerous chemical modifications of TFO are known. In pepti de nucleic acid (PNA), the sugar-phosphate backbone is replaced with a protein-like backbone. PNAs form P-loops while interacting with duple x DNA forming tripler with one of DNA strands leaving the other strand displaced. Very unusual recombination or parallel triplexes, or R-DNA , have been assumed to form under RecA protein in the course of homolo gous recombination.