~1J_(NH) Values Show that N1···N3 Hydrogen Bonds Are Stronger in dsRNA A:U than dsDNA A:T Base Pairs

摘要

Despite the well-established differences between RNA and DNA A- and B-form structures, it is still debatable whether there are differences in the hydrogen-bond lengths or strengths of RNA and DNA. The highest resolved X-ray crystal structures reveal no differences in hydrogen-bond lengths within uncertainty. It was shown in nonbase paired mononucleotides that the difference in pK_a values of rA and rU is less than that for values of dA and dT, from which it was inferred that RNA hydrogen bonds can be stronger than those of DNA. However, it has been shown that pK_a values of nucleobases can shift significantly upon base pairing. Trans-hydrogen bond deuterium isotope shifts of ~(13)C2 of adenines in Watson-Crick base pairs, ~(2h)Δ~(13)C2 (= δ~(13)C2{~1H3} -δ~(13)C2{~2H3}), of RNA were found to be more negative than in DNA, which implies that RNA hydrogen bonds are stronger. However, recent ab initio calculations have suggested that the difference between RNA and DNA ~(2h)Δ~(13)C2 yalues merely reflects the chemical difference between uracil and thymine rather than any difference in hydrogen-bond strengths.