title: X-ray analyses of d(GCGAXAGC) containing G and T at X: the base-intercalated duplex is still stable even in point mutants at the fifth residue.
abstract: DNA fragments containing the sequence d(GCGAAAGC) prefer to adopt a base-intercalated (zipper-like) duplex in the crystalline state. To investigate effects of point mutation at the 5th residue on the structure, two crystal structures of d(GCGAGAGC) and d(GCGATAGC) have been determined by X-ray crystallography. In the respective crystals, the two octamers related by a crystallographic two-fold symmetry are aligned in an anti-parallel fashion and associated to each other to form a duplex, suggesting that the base-intercalated duplex is stable even when the 5th residue is mutated with other bases. The sheared G3:A6 pair formation makes the two phosphate backbones closer and facilitates formation of the A-X*-X-A* base-intercalated motif. The three duplexes are assembled around the three-fold axis, and their 3rd and 4th residues are bound to the hexamine cobalt chloride. The central 5th residues are bound to another cation.
authors.affiliation: Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama 226-8501, Japan.
authors.forename: Jiro
authors.initials: J
authors.lastname: Kondo
authors.forename: Shun-ichi
authors.initials: S
authors.lastname: Umeda
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Fujita
authors.forename: Tomoko
authors.initials: T
authors.lastname: Sunami
authors.forename: Akio
authors.initials: A
authors.lastname: Takénaka
mesh_terms: D020029:Base Pairing; D001483:Base Sequence; D001665:Binding Sites; D003198:Computer Simulation; D006147:Guanine / Q000737:chemistry*; D007364:Intercalating Agents / Q000737:chemistry*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009841:Oligonucleotides / Q000737:chemistry*; D013941:Thymine / Q000737:chemistry*; D014961:X-Ray Diffraction / Q000379:methods*
chemical_list: D007364:Intercalating Agents; D009841:Oligonucleotides; D006147:Guanine; D013941:Thymine