title: Human telomeric C-strand tetraplexes.
abstract: Telomeric C-strand sequences form non-Watson-Crick base-paired structures in supercoiled plasmids and in oligonucleotides at low pH. Here we examine oligonucleotides composed of 2 or 4 repeats of the human telomeric C-strand sequence d(CCCTAA)n. At low pH, the 2-repeat molecule forms a dimer which exhibits H1'-H1' nuclear Overhauser effects (NOEs) between stacked CC+ base pairs. These NOEs are characteristic of the i-motif, which is a tetraplex composed of two intercalated CC+ duplexes. The 4-repeat molecule forms an intramolecular monomeric structure at low pH, suggesting that four contiguous cytosine tracts fold into a CC+ intercalated tetraplex. These unusual structures may be relevant to the formation of guanine tetraplexes by complementary G-rich sequences. They may also provide a general mechanism for self-recognition by nucleic acids.
authors.affiliation: Department of Zoology and Genetics, Iowa State University, Ames 50011, USA.
authors.forename: S
authors.initials: S
authors.lastname: Ahmed
authors.forename: A
authors.initials: A
authors.lastname: Kintanar
authors.forename: E
authors.initials: E
authors.lastname: Henderson
mesh_terms: D001483:Base Sequence; D004247:DNA / Q000737:chemistry*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009690:Nucleic Acid Conformation
chemical_list: D004247:DNA