title: Synthesis, structure and thermodynamic properties of 8-methylguanine-containing oligonucleotides: Z-DNA under physiological salt conditions.
abstract: Various oligonucleotides containing 8-methylguanine (m8G) have been synthesized and their structures and thermodynamic properties investigated. Introduction Of M8G into DNA sequences markedly stabilizes the Z conformation under low salt conditions. The hexamer d(CGC[M8G]CG)2 exhibits a CD spectrum characteristic of the Z conformation under physiological salt conditions. The NOE-restrained refinement unequivocally demonstrated that d(CGC[m8G]CG)2 adopts a Z structure with all guanines in the syn conformation. The refined NMR structure is very similar to the Z form crystal structure of d(CGCGCG)2, with a root mean square deviation of 0.6 between the two structures. The contribution of m8G to the stabilization of Z-DNA has been estimated from the mid-point NaCl concentrations for the B-Z transition of various m8G-containing oligomers. The presence of m8G in d(CGC[m8G]CG)2 stabilizes the Z conformation by at least deltaG = -0.8 kcal/mol relative to the unmodified hexamer. The Z conformation was further stabilized by increasing the number of m8Gs incorporated and destabilized by incorporating syn-A or syn-T, found respectively in the (A,T)-containing alternating and non-alternating pyrimidine-purine sequences. The results suggest that the chemically less reactive m8G base is a useful agent for studying molecular interactions of Z-DNA or other DNA structures that incorporate syn-G conformation.
authors.affiliation: Department of Synthetic Chemistry and Biological Chemistry, Faculty of Engineering, Kyoto University, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Sugiyama
authors.forename: K
authors.initials: K
authors.lastname: Kawai
authors.forename: A
authors.initials: A
authors.lastname: Matsunaga
authors.forename: K
authors.initials: K
authors.lastname: Fujimoto
authors.forename: I
authors.initials: I
authors.lastname: Saito
authors.forename: H
authors.initials: H
authors.lastname: Robinson
authors.forename: A H
authors.initials: AH
authors.lastname: Wang
mesh_terms: D001483:Base Sequence; D002942:Circular Dichroism; D004247:DNA / Q000737:chemistry*; D006147:Guanine / Q000031:analogs & derivatives* / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D013816:Thermodynamics
chemical_list: D009838:Oligodeoxyribonucleotides; C066771:8-methylguanine; D006147:Guanine; D004247:DNA