title: Ionized and wobble base-pairing for bromouracil-guanine in equilibrium under physiological conditions. A nuclear magnetic resonance study on an oligonucleotide containing a bromouracil-guanine base-pair as a function of pH.
abstract: A one and two-dimensional nuclear magnetic resonance study of a non-selfcomplementary oligonucleotide containing a central 5-bromouracil-guanine pair is reported. For these two bases three types of hydrogen bonding schemes could exist; wobble, rare tautomer and ionized. The two-dimensional spectra of non-exchangeable protons together with one-dimensional spectra recorded in water show that at pH 7.0 the predominant species is a right-handed B-form DNA in which the brU.G pair has wobble geometry. On raising the pH we observe a transition monitored by proton chemical shift changes for the brU.G and adjacent base-pairs. The mid-point of the transition was observed at pH 8.6. Spectra recorded at pH 9.8 show that the helix remains intact with B form conformation. It is shown that this high pH form has an ionized brU.G base-pair now in Watson-Crick geometry. Thus under physiological conditions an equilibrium exists between wobble and ionized structures.
authors.affiliation: Department of Biological Sciences, University of Southern California, Los Angeles 90089-1481.
authors.forename: L C
authors.initials: LC
authors.lastname: Sowers
authors.forename: M F
authors.initials: MF
authors.lastname: Goodman
authors.forename: R
authors.initials: R
authors.lastname: Eritja
authors.forename: B
authors.initials: B
authors.lastname: Kaplan
authors.forename: G V
authors.initials: GV
authors.lastname: Fazakerley
mesh_terms: D001482:Base Composition; D001976:Bromouracil / Q000378:metabolism*; D006147:Guanine / Q000378:metabolism*; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D009841:Oligonucleotides / Q000378:metabolism*; D011522:Protons
chemical_list: D009841:Oligonucleotides; D011522:Protons; D001976:Bromouracil; D006147:Guanine