Sequence-dependent conformational heterogeneity of a hybrid DNA.RNA dodecamer duplex

Two- and three-dimensional homonuclear NMR studies of a hybrid duplex RI, formed by annealing r(GCGCAAAACGCG) and d(CGCGTTTTGCGC) strands are described. NMR parameters, such as intra- and interresidue proton-proton NOEs and sugar proton coupling constants were analyzed with reference to those of the corresponding DNA.DNA duplex. Furthermore, spectral analyses were conducted on the basis of model structures of nucleic acid duplexes. Distinctive spectral patterns of the hybrid duplex reveal unique heterogeneous conformations which co-exist throughout the sequence and are significantly different from those of model structures of either canonical A- or B-forms. Features of an intermediate conformation were observed in the DNA and RNA strands in duplex RI, the former being more B-like and the latter more A-like. Three-dimensional NOESY-NOESY spectra were analyzed and their use was demonstrated for resolving superimposed resonances and cross peaks, especially those originating from the RNA strand. The application of a useful strategy that combines the use of 2D NMR data and the known structural information for efficient 3D spectral analyses is demonstrated.