title: NMR studies of G:A mismatches in oligodeoxyribonucleotide duplexes modelled after ribozymes.
abstract: The structures of two oligodeoxyribonucleotide duplexes, the base sequences of which were modelled after both a hammerhead ribozyme and a small metalloribozyme, were studied by NMR. Both duplexes contain adjacent G:A mismatches; one has a PyGAPu:PyGAPu sequence and the other a PyGAPy:PuGAPu sequence. It is concluded on the basis of many characteristic NOEs that in both duplexes G:A base pairs are formed in the unique 'sheared' form, where an amino proton instead of an imino proton of G is involved in the hydrogen bonding, and G and A bases are arranged 'side by side' instead of 'head to head'. A photo-CIDNP experiment, which gives unique and independent information on the solvent accessibility of nucleotide bases, also supports G:A base pairing rather than a bulged-out structure of G and A residues. This is the first demonstration that not only the PyGAPu:PyGAPu sequence but also the PyGAPy:PuGAPu sequence can form the unique sheared G:A base pairs. Taking the previous studies on G:A mismatches into account, the idea is suggested that a PyGA:GAPu sequence is a minimum and essential element for the formation of the sheared G:A base pairs. The sheared G:A base pairs in the PyGAPu:PyGAPu sequence are suggested to be more stable than those in the PyGAPy:PuGAPu sequence. This is explained rationally by the idea proposed above.
authors.affiliation: Department of Bioengineering, Faculty of Engineering, Yokohama National University, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Katahira
authors.forename: H
authors.initials: H
authors.lastname: Sato
authors.forename: K
authors.initials: K
authors.lastname: Mishima
authors.forename: S
authors.initials: S
authors.lastname: Uesugi
authors.forename: S
authors.initials: S
authors.lastname: Fujii
mesh_terms: D001483:Base Sequence; D002384:Catalysis; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides / Q000737:chemistry*; D016337:RNA, Catalytic / Q000737:chemistry*
chemical_list: D009838:Oligodeoxyribonucleotides; D016337:RNA, Catalytic