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

L. C. Sowers, M. F. Goodman, R. Eritja, B. Kaplan, G. V. Fazakerley

Research output: Contribution to journalArticle

73 Scopus citations


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 onedimensional 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.

Original languageEnglish (US)
Pages (from-to)437-447
Number of pages11
JournalJournal of Molecular Biology
Issue number2
StatePublished - Jan 20 1989
Externally publishedYes


ASJC Scopus subject areas

  • Structural Biology
  • Molecular Biology

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