Structure analyses of DNA oligomers by use of heteronuclear 2D NMR

DNA oligomer d(CGGAAGACTCTCCTCCG):d(CGGAGGAGAGTCTTCCG) named UASG (17mer M.W. = 11 kDa) was studied by 1H NMR and heteronuclear two dimensional (2D) NMR. All the labile protons and half of the non-exchangeable protons were assigned by use of conventional 1H 2D experiments including NOESY using 1-1 echo excitation for water suppression. Signal degeneracy in the sugar proton region made it difficult to make assignments of the remaining half of the non-exchangeable protons of the oligomer in 1H 2D spectra. Here we report a new strategy using 1H/13C and 1H/31P heteronuclear single-quantum correlation spectroscopy combined with homonuclear three dimensional NOESY-TOCSY. By this strategy, most of the proton resonances of the oligomer have been assigned, and it turned out that the whole conformation of the oligomer is B-form like.