title: Structural competition involving G-quadruplex DNA and its complement.
abstract: Structural competition between the G-quadruplex, the I-motif, and the Watson-Crick duplex has been implicated for repetitive DNA sequences, but the competitive mechanism of these multistranded structures still needs to be elucidated. We investigated the effects of sequence context, cation species, and pH on duplex formation by the G-quadruplex of dG(3)(T(2)AG(3))(3) and its complement the I-motif of d(C(3)TA(2))(3)C(3), using ITC, DSC, PAGE, CD, UV, and CD stopped-flow kinetic techniques. ITC and PAGE experiments confirmed Watson-Crick duplex formation by the complementary strands. The binding constant of the two DNA strands in the presence of 10 mM Mg(2+) at pH 7.0 was shown to be 5.28 x 10(7) M(-1) at 20 degrees C, about 400 times larger than that in the presence of 100 mM Na(+) at pH 5.5. The dynamic transition traces of the duplex formation from the equimolar mixture of G-/C-rich complementary sequences were obtained at both pH 7.0 and pH 5.5. Fitting to a single-exponential function gave an observed rate of 8.06 x 10(-3) s(-1) at 20 degrees C in 10 mM Mg(2+) buffer at pH 7.0, which was about 10 times the observed rate at pH 5.5 under the same conditions. Both of the observed rates increased as temperature rose, implying that the dissociation of the single-stranded structured DNAs is the rate-limiting step for the WC duplex formation. The difference between the apparent activation energy at pH 7.0 and that at pH 5.5 reflects the fact that pH significantly influences the structural competition between the G-quadruplex, the I-motif, and the Watson-Crick duplex, which also implies a possible biological role for I-motifs in biological regulation.
authors.affiliation: High Technology Research Center, Konan University, 8-9-1 Okamoto, Higashinada-ku, Kobe 658-8501, Japan.
authors.forename: Wei
authors.initials: W
authors.lastname: Li
authors.forename: Daisuke
authors.initials: D
authors.lastname: Miyoshi
authors.forename: Shu-ichi
authors.initials: S
authors.lastname: Nakano
authors.forename: Naoki
authors.initials: N
authors.lastname: Sugimoto
mesh_terms: D000818:Animals; D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D004247:DNA / Q000737:chemistry*; D004277:DNA, Single-Stranded / Q000737:chemistry; D004591:Electrophoresis, Polyacrylamide Gel; D024202:Electrophoretic Mobility Shift Assay; D054856:G-Quadruplexes; D006801:Humans; D007700:Kinetics; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D009692:Nucleic Acid Heteroduplexes / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D013329:Structure-Activity Relationship; D013816:Thermodynamics
chemical_list: D004277:DNA, Single-Stranded; D009692:Nucleic Acid Heteroduplexes; D004247:DNA