Conformational Analysis of the Single-Stranded Ribonucleic Acid A-A-C-C. A One-Dimensional and Two-Dimensional Proton NMR Study at 500 MHz

Abstract

1H NMR studies at 300 MHz and 500 MHz are reported on the ribotetranucleotide AACC. The complete 1H NMR spectral assignment at 20.degree. C is given. Two-dimensional NMR was used to elucidate spin multiplets in crowded regions. Nuclear Overhauser enhancement (NOE) experiments made an unambiguous spectral assignment possible and yielded information on interproton distances. The N/S equilibrium of the riboses and the rotamer populations around some backbone torsion angles are presented. A large preference for N-type ribose and .gamma.+ and .beta.t backbone torsions is observed, in particular in the central A-C unit of AACC. Information on distances between protons of different nucleotide units, obtained from NOE experiments, constitutes a probe of base-base stacking. AACC offers a good model for RNA single-strand conformation.