Triplex DNA structures

Annu Rev Biochem. 1995;64:65-95. doi: 10.1146/


A DNA triplex is formed when pyrimidine or purine bases occupy the major groove of the DNA double Helix forming Hoogsteen pairs with purines of the Watson-Crick basepairs. Intermolecular triplexes are formed between triplex forming oligonucleotides (TFO) and target sequences on duplex 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 activity in vivo. Numerous chemical modifications of TFO are known. In peptide nucleic acid (PNA), the sugar-phosphate backbone is replaced with a protein-like backbone. PNAs form P-loops while interacting with duplex DNA forming triplex 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 homologous recombination.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Review

MeSH terms

  • Animals
  • DNA / chemistry*
  • DNA / genetics
  • Drug Stability
  • Humans
  • Molecular Structure
  • Nucleic Acid Conformation*
  • Nucleic Acids / chemistry
  • Peptides / chemistry
  • Recombination, Genetic


  • Nucleic Acids
  • Peptides
  • triplex DNA
  • DNA