title: Parallel double stranded helices and the tertiary structure of nucleic acids.
abstract: Thermal denaturation of four oligonucleotides, viz. 3'-d(AT)5pO(CH2)6Opd(AT)5-3'(par(AT], 3'-d(AT)5pO(CH2)6Opd(AT)5-5'(anti(AT],3'-d(A)10pO(CH2) 6Op(T)10-3'(par(A-T], and 3'-d(A)10pO(CH2)6Opd(T)10-5' (anti(A-T], was studied in 0.01 M phosphate buffer, pH 7, in the presence of 0.1, 0.25, 0.5 and 1.0 M NaCl. All the oligomers were found to exist at a lower temperature (0 to 20 degrees C) as complexes composed either of two oligomer molecules (a canonical duplex) or of more oligomer molecules whereas, at a higher temperature (30 to 70 degrees C), they formed hairpins with a parallel (par(AT) and par(A-T] or antiparallel (anti(AT) and anti(A-T) orientation of the chains. Melting curves (A260(T] were used to calculate thermodynamic parameters for the formation of hairpins and "low-temperature" duplexes. Experiments on ethidium bromide binding to the oligonucleotides have shown that the oligomer anti(A-T) exists, at a low ionic strength, as a four stranded complex ("quadruplex") contains two antiparallel helices, d(A).d(T), which have a parallel orientation and are bound to one another owing to the formation of additional hydrogen bonds between nucleic acid bases. The possible biological function of quadruplexes is discussed.
authors.affiliation: V.A. Engelhardt Institute of Molecular Biology USSR Academy of Sciences, Moscow.
authors.forename: O F
authors.initials: OF
authors.lastname: Borisova
authors.lastname: Golova YuB
authors.forename: B P
authors.initials: BP
authors.lastname: Gottikh
authors.forename: A S
authors.initials: AS
authors.lastname: Zibrov
authors.forename: I A
authors.initials: IA
authors.lastname: Il'icheva
authors.lastname: Lysov YuP
authors.forename: O K
authors.initials: OK
authors.lastname: Mamayeva
authors.forename: B K
authors.initials: BK
authors.lastname: Chernov
authors.forename: A A
authors.initials: AA
authors.lastname: Chernyi
authors.forename: A K
authors.initials: AK
authors.lastname: Shchyolkina
mesh_terms: D001483:Base Sequence; D002151:Calorimetry; D004247:DNA / Q000737:chemistry*; D006860:Hydrogen Bonding; D007700:Kinetics; D046911:Macromolecular Substances; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D009838:Oligodeoxyribonucleotides / Q000737:chemistry*; D009843:Oligoribonucleotides / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics
chemical_list: D046911:Macromolecular Substances; D009838:Oligodeoxyribonucleotides; D009843:Oligoribonucleotides; D004247:DNA