title: Unique quadruplex structures of d(GGA)4 (12-mer) and d(GGA)8 (24-mer)--direct evidence of the formation of non-canonical base pairs and structural comparison.
abstract: We have reported that d(GGA)4 (12-mer) folds into an intramolecular parallel quadruplex with a G:G:G:G tetrad and a G(:A):G(:A):G(:A):G heptad and that two quadruplexes form a dimer. Here we present the unique structure of d(GGA)8 (24-mer) under physiological conditions. G1-A12 and G13-A24 segments of d(GGA)8 fold into an intramolecular parallel quadruplex with the tetrad and heptad, respectively, and two quadruplexes stack each other in a head-to-head manner. The formation of non-canonical G:G and G:A base pairs was directly certified by observing spin-spin couplings across hydrogen bonds with the aid of 13C-, 15N-labelling of DNA. It was noted that the monomeric architecture of d(GGA)8 resembles the dimeric architecture of d(GGA)4. Interestingly, the recent X-ray study shows that the telomere DNA also folds into the similar intramolecular parallel quadruplex as we have reported for GGA-repeat DNAs.
authors.affiliation: Graduate School of Environment and Information Sciences, Yokohama National University, 79-7 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan.
authors.forename: Akimasa
authors.initials: A
authors.lastname: Matsugami
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Ouhashi
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Ikeda
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Okuizumi
authors.forename: Hidetsugu
authors.initials: H
authors.lastname: Sotoya
authors.forename: Seiichi
authors.initials: S
authors.lastname: Uesugi
authors.forename: Masato
authors.initials: M
authors.lastname: Katahira
mesh_terms: D020029:Base Pairing; D009690:Nucleic Acid Conformation; D009841:Oligonucleotides / Q000737:chemistry*
chemical_list: D009841:Oligonucleotides