Triple helix formation and homologous strand exchange in pyrene-labeled oligonucleotides.
The orientations of the symmetrical third strands (G3A4G3) and (G3T4G3) within the triplexes (C3T4C3) - (G3A4G3) x (G3A4G3) and (C3T4C3) - (G3A4G3) x (G3T4G3) were investigated by fluorescence spectroscopy and thermal denaturation using pyrene-labeled oligodeoxynucleotides. In the two triplex structures, both parallel and antiparallel orientations of the third strand with respects to the purine Watson-Crick one were identified by means of pyrene excimer formation. The pyrene labels do not modify the melting temperature of the (C3T4C3) - (G3A4G3) x (G3T4G3) triplex but somewhat stabilize the corresponding duplex against thermal denaturation. The absorption melting profiles of the (C3T4C3) - (G3A4G3) x (G3A4G3) triplex are monophasic in agreement with previous reports. In contrast, the melting of this structure, when monitored by the pyrene excimer band, reveals a biphasic behavior. These data, together with kinetics measurements, strongly suggest exchange mechanisms between the homologous oligomers (G3A4G3), Hoogsteen, and Watson-Crick strands.
Mohammadi
S
S
Laboratoire de Spectroscopie Biomoléculaire, URA CNRS 1430, UFR de Médecine et Biologie Humaine, Université Paris XIII, Bobigny, France.
Slama-Schwok
A
A
Léger
G
G
el Manouni
D
D
Shchyolkina
A
A
Leroux
Y
Y
Taillandier
E
E
D004247:DNA / Q000737:chemistry*; D005456:Fluorescent Dyes; D008956:Models, Chemical; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D009838:Oligodeoxyribonucleotides / Q000737:chemistry*; D011721:Pyrenes / Q000737:chemistry; D011995:Recombination, Genetic
D005456:Fluorescent Dyes; D009838:Oligodeoxyribonucleotides; D011721:Pyrenes; C051802:triplex DNA; D004247:DNA