NMR study of a novel RNA quadruplex structure

The structure of an RNA oligomer, r (GGAGGUUUUGGAGG) (R14-2) whose G-G steps are separated by adenine and uracil residues has been investigated by NMR. In the presence of 20 mM K+, a novel dimeric multiplex architecture is adopted by two strands of R14-2. In each strand a UUUU loop and two A residues connect four parallel G-G steps that pair-align into two tetrads. One of the tetrads is further pair-aligned by two A residues through the sheared mismatch and a novel hexad is subsequently formed. Two hexads coming from two different strands stack to make a dimeric multiplex. All of the guanosine and adenosine residues take an anti conformation.