Evidence for A+(anti)–G(syn) mismatched base–pairing in d–GGTAAGCGTACC

Two-dimensional NMR spectroscopy has been used to study the structure and hydrogen bonding scheme of A:G mismatched base pairing in d-GGTAAGCGTACC at pH 5.8. Under the conditions of our study, the molecule forms a B-DNA helix, with the mismatched bases in the A+ anti)-G(syn) conformation. The adenosine exists in the protonated form. The NOESY spectrum in 90% H2O + 10% 2H2O has been used to assign all observable imino and amino protons including those involved in the A+(anti)-G(syn) base pair. Both the proton donors in the A:G mismatched inter-base hydrogen bonding are situated on adenosine.