title: Chemical modification of pyrimidine TFOs: effect on i-motif and triple helix formation.
abstract: In order to form more stable triple helical structures or to prevent their degradation in cells, oligonucleotide analogs are routinely used, either in the backbone or among the bases. The target sequence chosen for this study is a 16-base-long oligopurine-oligopyrimidine region present in the human neurotrophin 4/5 gene. Seven different chemical modifications were tested for their effect on (i) triple helix formation and (ii) i-DNA stability. i-DNA is a tetrameric structure involving hemiprotonated C x C+ base pairs, which may act as a competing structure for triplex formation, especially in the case of a cytosine-rich third strand. At acid pH, oligophosphoramidates formed the most stable triple helix, whereas oligonucleotides including 5-propynyl-dU formed a stable i-motif which precluded triplex formation. Only two candidates stabilized triple helices at neutral pH: oligonucleotides with phosphoramidate linkage and phosphodiester oligonucleotides containing 5-methyl-dC and 5-propynyl-dU.
authors.affiliation: Laboratoire de Biophysique, Muséum National d'Historie Naturelle, INSERM U201, CNRS UMR 8646, Paris, France.
authors.forename: L
authors.initials: L
authors.lastname: Lacroix
authors.forename: J L
authors.initials: JL
authors.lastname: Mergny
mesh_terms: D001483:Base Sequence; D004247:DNA / Q000737:chemistry / Q000235:genetics; D004355:Drug Stability; D006801:Humans; D066298:In Vitro Techniques; D009414:Nerve Growth Factors / Q000235:genetics; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D009838:Oligodeoxyribonucleotides / Q000737:chemistry* / Q000235:genetics; D011743:Pyrimidines / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet; D013816:Thermodynamics
chemical_list: D009414:Nerve Growth Factors; D009838:Oligodeoxyribonucleotides; D011743:Pyrimidines; D004247:DNA