title: NMR observation of T-tetrads in a parallel stranded DNA quadruplex formed by Saccharomyces cerevisiae telomere repeats.
abstract: We report here the NMR structure of the DNA sequence d-TGGTGGC containing two repeats of Saccharomyces cerevisiae telomere DNA which is unique in that it has a single thymine in the repeat sequence and the number of Gs can vary from one to three. The structure is a novel quadruplex incor-porating T-tetrads formed by symmetrical pairing of four Ts via O4-H3 H-bonds in a plane. This is in contrast to the previous results on other telomeric sequences which contained more than one T in the repeat sequences and they were seen mostly in the flexible regions of the structures. We observed that the T4-tetrad was nicely accommodated in the center of the G-quadruplex, but it caused a small underwinding of the right handed helix. The T tetrad stacked well on the adjacent G3-tetrad, but poorly on the G5 tetrad. Likewise, T1 also formed a stable T-tetrad at the 5' end of the quadruplex. To our knowledge, this is the first report of T-tetrad formation in DNA structures. These observations are of significance from the points of view of both structural diversity and specific recognitions.
authors.affiliation: Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India.
authors.forename: P K
authors.initials: PK
authors.lastname: Patel
authors.forename: R V
authors.initials: RV
authors.lastname: Hosur
mesh_terms: D004271:DNA, Fungal / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D011188:Potassium / Q000737:chemistry; D012091:Repetitive Sequences, Nucleic Acid; D012441:Saccharomyces cerevisiae / Q000737:chemistry* / Q000235:genetics; D016615:Telomere / Q000737:chemistry*
chemical_list: D004271:DNA, Fungal; D011188:Potassium