title: [5mCCTCTCTCC]4: an i-motif tetramer with intercalated T*T pairs.
abstract: The i-motif is a four-stranded structure built by intercalation in a head-to-tail orientation of two parallel duplexes associated by hemiprotonated C(*)C(+) pairs. T*T pairs are nearly isomorphic of C*C(+) pairs; however the structural investigations of i-motif tetramers containing thymidines suggest that the i-motif cannot accommodate T*T pairs in a face-to-face orientation. The tetramer of 5mCCTCTCTCC make an exception. It includes two symmetry related open/closed T3/T7 groups, but the central thymidines form two long-lived T5*T5 pairs that are intercalated in a face-to-face orientation. This observation provides indications of the origin of the conflict that usually hinders T*T intercalation into i-motif structures and more generally of the constraints influencing i-motif formation.
authors.affiliation: Laboratoire de Chimie et Biologie Structurale, Institut de Chimie des Substances Naturelles, Gif-sur-Yvette, France 91190.
authors.forename: Muriel
authors.initials: M
authors.lastname: Canalia
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Leroy
mesh_terms: D020029:Base Pairing; D001483:Base Sequence; D004247:DNA / Q000737:chemistry*; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D009690:Nucleic Acid Conformation; D013936:Thymidine / Q000737:chemistry*
chemical_list: D004247:DNA; D013936:Thymidine