Applications of tritium NMR to macromolecules: a study of two nucleic acid molecules.

We have tritium labeled two nucleic acid molecules, an 8 kDa DNA oligomer and a 20 kDa 'hammer-head' RNA for tritium NMR investigations. The DNA sequence studied has been previously used in homonuclear studies of DNA-bound water molecules and tritium NMR was expected to facilitate these investigations by eliminating the need to suppress the water resonance in tritium-detected 3H-1H NOESY experiments. We observed the anticipated through-space interactions found in B-form DNA in the NOESY experiments and an unexpected 'antiphase' cross-peak at the water frequency. T1 measurements on the tritiated DNA molecule indicated that relaxation rates were also accelerated for tritium and protons. Tritium NMR spectra of the hammerhead RNA molecule indicated conformational dynamics in the conserved region of the molecule in the absence of Mg2+ and spermine, two components necessary for cleavage. The dynamics were also investigated by 15N-correlated 1H spectroscopy and persisted after the addition of Mg2+ and spermine.