N1…N3 Hydrogen Bonds of A:U Base Pairs of RNA Are Stronger than Those of A:T Base Pairs of DNA

摘要

RNA and DNA are different structurally and functionally, and much effort has gone into elucidating the physical and chemical bases of these differences. Although it is well accepted that hydrogen bonds are central to the structure and function of nucleic acids, it is not yet clear whether significant differences exist between RNA and DNA hydrogen bonds. Amplitudes of fast purine librations were found to be similar in homologous RNA and DNA duplexes. Imino proton exchange comparisons show that base-pair lifetimes of RNA A:U base pairs are shorter than those of DNA A:T base pairs. However, base-pair kinetics are not exclusively a function of hydrogen bonding but also of base stacking interactions. Recently, it was shown in non-base-paired mononucleotides that the difference in pK_a values of rA and rU is less than that for dA and dT, from which it was inferred that RNA hydrogen bonds can be stronger than those of DNA. Trans-hydrogen-bond scalar couplings, which reflect the extent of electron delocalization across the hydrogen bond, have been measured in RNA and DNA duplexes and triplexes. However, the RNA and DNA sequences were not homologous, and a comparison of the distribution of ~(2h)J_(NN) values did not reveal any differences.