title: Sheared-type G(anti).C(syn) base-pair: a unique d(GXC) loop closure motif.
abstract: Stable DNA loop structures closed by a novel G.C base-pair have been determined for the single-residue d(GXC) loops (X=A, T, G or C) in low-salt solution by high-resolution nuclear magnetic resonance (NMR) techniques. The closing G.C base-pair in these loops is not of the canonical Watson-Crick type, but adopts instead a unique sheared-type (trans Watson-Crick/sugar-edge) pairing, like those occurring in the sheared mismatched G.A or A.C base-pair, to draw the two opposite strands together. The cytidine residue in the closing base-pair is transformed into the rare syn domain to form two H-bonds with the guanine base and to prevent the steric clash between the G 2NH(2) and the C H-5 protons. Besides, the sugar pucker of the syn cytidine is still located in the regular C2'-endo domain, unlike the C3'-endo domain adopted for the pyrimidines of the out-of-alternation left-handed Z-DNA structure. The facile formation of the compact d(GXC) loops closed by a unique sheared-type G(anti).C(syn) base-pair demonstrates the great potential of the single-stranded d(GXC) triplet repeats to fold into stable hairpins.
authors.affiliation: Institute of Biochemistry, National Chung-Hsing University, Taichung, Taiwan, ROC.
authors.forename: Ko-Hsin
authors.initials: KH
authors.lastname: Chin
authors.forename: Shan-Ho
authors.initials: SH
authors.lastname: Chou
mesh_terms: D020029:Base Pairing; D004247:DNA / Q000737:chemistry*; D006801:Humans; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D010710:Phosphates / Q000737:chemistry
chemical_list: D009838:Oligodeoxyribonucleotides; D010710:Phosphates; D004247:DNA