title: Structural analysis of Z-Z DNA junctions with A:A and T:T mismatched base pairs by NMR.
abstract: Left-handed Z-DNA structure is favored by the alternating (dC-dG)n sequence. Many Z-potentiating sequences are found in genome and they often do not have a perfect alternating (dC-dG)n sequence. When a single base pair is removed from the alternating (dC-dG)n sequence, a Z-Z junction is created. A Z-Z junction is energetically less favorable by 3.5 kcal/mol than a perfect Z-DNA sequence. We designed special sequences to probe the structural perturbation at the Z-Z junction. Four DNA oligomers, d(*CG*CGT*CG*CG) and d(*CG*CGA*CG*CG) (*C = C or br5C), have been synthesized and analyzed by NMR. The two br5C-modified DNA nonamers are in the Z-DNA conformation in 50% methanol solution. The T and the A nucleotides are in the anti and syn conformation, respectively, in the two br5C nonamers. The NOE-restrained molecular dynamics refinement demonstrated that T-T and A-A bases in the two Z-DNA duplexes are dynamic and adopt a range of conformations. Mixing the br5C-d(*CG*CGT*CG*CG) and br5C-d(*CG*CGA*CG*CG) nonamers together converts a fraction of the two nonamer populations into a hetero duplex as evident from the presence of the imino proton (at 13.70 ppm) of an A:T base pair. A model has been generated for the br5C-d(*CG*CGT*CG*CG)+br5C-d(*CG*CGA*CG*CG) duplex which incorporates a Z-Z junction. Previous biophysical and biochemical data associated with the Z-Z junction are discussed in the context of the present model.
authors.affiliation: Department of Cell & Structural Biology, University of Illinois at Urbana-Champaign, Urbana 61801, USA.
authors.forename: X L
authors.initials: XL
authors.lastname: Yang
authors.forename: A H
authors.initials: AH
authors.lastname: Wang
mesh_terms: D000225:Adenine / Q000737:chemistry; D001482:Base Composition; D004247:DNA / Q000737:chemistry* / Q000378:metabolism; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D000432:Methanol / Q000494:pharmacology; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides / Q000138:chemical synthesis / Q000737:chemistry; D013941:Thymine / Q000737:chemistry
chemical_list: D009838:Oligodeoxyribonucleotides; D004247:DNA; D000225:Adenine; D013941:Thymine; D000432:Methanol