title: Cystosine-rich strands of the insulin minisatellite adopt hairpins with intercalated cytosine+.cytosine pairs.
abstract: Previously, we reported the high resolution NMR structure of the hairpin G-quartet structure formed by the G-rich strand of the insulin minisatellite of repeat sequence, (ACAG4TGTG4/TGTC4ACAC4) located upstream of the human insulin gene. Here, we report structural studies on the C-rich strand of this insulin minisatellite. First, we show by high resolution NMR that (C4TGTC4) forms a hairpin dimer with intercalated C+.C pairs (referred to as the hairpin i-motif); 340 NOE distance constraints uniquely define the nature of hairpin folding and the pattern of C+.C intercalation. Second, we show by one-dimensional NMR spectroscopy and molecular modeling studies that (C4TGTC4ACA4TGTC4) forms an intramolecularly folded hairpin with intercalated C+.C pairs. Third, we demonstrate by in vitro replication studies that several such hairpin i-motifs are present in long (C4TGTC4ACA)n (n>/=6) sequences, even in the presence of their complementary strands. Finally, we discuss structural and biological significance of the hairpin i-motifs formed by the C-rich strands of the insulin minisatellite.
authors.affiliation: Theoretical Biology and Biophysics, T-10, MS-K710, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.
authors.forename: P
authors.initials: P
authors.lastname: Catasti
authors.forename: X
authors.initials: X
authors.lastname: Chen
authors.forename: L L
authors.initials: LL
authors.lastname: Deaven
authors.forename: R K
authors.initials: RK
authors.lastname: Moyzis
authors.forename: E M
authors.initials: EM
authors.lastname: Bradbury
authors.forename: G
authors.initials: G
authors.lastname: Gupta
mesh_terms: D001483:Base Sequence; D003198:Computer Simulation; D003596:Cytosine / Q000737:chemistry*; D004261:DNA Replication; D004259:DNA-Directed DNA Polymerase / Q000378:metabolism; D019281:Dimerization; D006801:Humans; D007328:Insulin / Q000235:genetics*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D018598:Minisatellite Repeats; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides / Q000737:chemistry*
chemical_list: D007328:Insulin; D009838:Oligodeoxyribonucleotides; D003596:Cytosine; C034970:bacteriophage T7 induced DNA polymerase; D004259:DNA-Directed DNA Polymerase