Hairpin and parallel quartet structures for telomeric sequences

Nucleic Acids Res. 1992 Aug 11;20(15):4061-7. doi: 10.1093/nar/20.15.4061.


The role of thymine residues in the formation of G-quartet structures for telomeric sequences has been investigated using model oligonucleotides of the type d(G4TnG4), with n = 1-4. Sequences d(G4T3G4) and d(G4T4G4) adopt a G-quartet structure formed by hairpin dimerization in 70 mM NaCl as judged by a characteristic circular dichroism signature with a 295 nm positive and 265 nm negative bands while d(G4TG4) adopts a parallel G-quartet structure like d(G12) which exhibits a strong positive band at 260 nm and a negative band at 240 nm. The sequence d(G4T2G4) exhibits a mixture of both conformations. The stability of hairpin G-quartet structures decreases with decrease in the number of intervening thymine residues. Potassium permanganate, a single strand specific probe has been used to establish the presence of loops composed of T residues in the hairpin G quartet structures formed by the oligonucleotides d(G4TnG4) with n = 2-4 in 70 mM NaCl. The formation of hairpin G quartet structure for the above sequences is further supported by the enhanced electrophoretic mobility observed on non-denaturing polyacrylamide gels. Human telomeric sequence d(TTAGGG)4 which showed enhanced electrophoretic mobility like Tetrahymena telomeric sequence d(T2G4)4 also exhibited a characteristic CD spectrum for a folded-back G-quartet structure. A detailed model for G-quartet structure involving hairpin dimer with alternating syn-anti-syn-anti conformation for the guanine residues both along the chain as well as around the G tetrad with at least two thymine residues in the loop is proposed. Intermolecular association of short telomeric sequences reported here provides a possible model for chromosomal pairing.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Base Sequence
  • Circular Dichroism
  • Electrophoresis
  • Humans
  • Molecular Sequence Data
  • Nucleic Acid Conformation*
  • Oligodeoxyribonucleotides / genetics
  • Oligodeoxyribonucleotides / metabolism
  • Repetitive Sequences, Nucleic Acid / genetics
  • Spectrophotometry
  • Telomere*
  • Temperature
  • Tetrahymena / genetics


  • Oligodeoxyribonucleotides