title: Crystal structures of a DNA octaplex with I-motif of G-quartets and its splitting into two quadruplexes suggest a folding mechanism of eight tandem repeats.
abstract: Recent genomic analyses revealed many kinds of tandem repeats of specific sequences. Some of them are related to genetic diseases, but their biological functions and structures are still unknown. Two X-ray structures of a short DNA fragment d(gcGA[G]1Agc) show that four base-intercalated duplexes are assembled to form an octaplex at a low K+ concentration, in which the eight G5 residues form a stacked double G-quartet in the central part. At a higher K+ concentration, however, the octaplex is split into just two halves. These structural features suggest a folding process of eight tandem repeats of d(ccGA[G]4Agg), according to a double Greek-key motif. Such a packaging of the repeats could facilitate slippage of a certain sequence during DNA replication, to induce increase or decrease of the repeats.
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: Wataru
authors.initials: W
authors.lastname: Adachi
authors.forename: Shun-ichi
authors.initials: S
authors.lastname: Umeda
authors.forename: Tomoko
authors.initials: T
authors.lastname: Sunami
authors.forename: Akio
authors.initials: A
authors.lastname: Takénaka
mesh_terms: D001483:Base Sequence; D018360:Crystallography, X-Ray; D004247:DNA / Q000737:chemistry* / Q000235:genetics*; D054856:G-Quadruplexes; D018598:Minisatellite Repeats / Q000235:genetics; D008958:Models, Molecular; D009690:Nucleic Acid Conformation / Q000187:drug effects; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D020080:Tandem Repeat Sequences / Q000235:genetics*; D013816:Thermodynamics; D014867:Water / Q000378:metabolism
chemical_list: D014867:Water; D004247:DNA; D011188:Potassium