title: 1H NMR assignments and conformational analysis of the oligoribonucleotides CA, CAU, CAUG, ACAUG, and UCAUG: observation of pyrimidine H5-H1' long-range scalar couplings.
abstract: Conformational analysis and 1H NMR spectral assignments have been carried out using COSY and RELAY methods for a series of related oligoribonucleotides including two pentamers with 5'-dangling bases. Intraresidue long-range five bond scalar coupling was observed between pyrimidine H5 and H1' protons in the COSY-45 spectra and this feature was useful for both assignment purposes and conformational analysis. The ribose ring conformations were predominantly C3'-endo with the C2'-endo population increasing at the 3'-terminus. The 5'-dangling bases were not stacked efficiently, exhibiting lower % C3'-endo values than their 3'-nearest neighbors. Backbone torsion angle population. beta t, gamma +, epsilon t, were determined using 1H-1H, 1H-31P, and 13C-31P coupling constants. From beta t and gamma + populations the U3-G4 step in CAUG was found to be less efficiently stacked than the C1-A2 and A2-U3 steps. This observation in solution is consistent with the fiber diffraction A-RNA model (S. Arnott, D.W.L. Hukins, S.D. Dover, W. Fuller and A.R. Hodgson, J. Mol. Biol. 81, 107-122, 1973) which also predicts poor stacking in a U-G dinucleotide. The epsilon t populations were greater than 65% for all C3'-O3' bonds and consistent with a right-handed A-RNA helix.
authors.affiliation: Department of Chemistry, McMaster University, Hamilton, Ontario, Canada.
authors.forename: J
authors.initials: J
authors.lastname: Orban
authors.forename: R A
authors.initials: RA
authors.lastname: Bell
mesh_terms: D001483:Base Sequence; D009682:Magnetic Resonance Spectroscopy; D009690:Nucleic Acid Conformation; D009843:Oligoribonucleotides; D011743:Pyrimidines
chemical_list: D009843:Oligoribonucleotides; D011743:Pyrimidines