Conformational mobility of deoxyribonucleic acid, transfer ribonucleic acid, and poly(adenylic acid) as monitored by carbon-13 nuclear magnetic resonance relaxation.

The molecular motion of DNA, the native form of tRNA, and partially denatured poly(A) has been investigated by carbon-13 nuclear magnetic resonance (13C NMR). The nuclear Overhauser effect of the RNA samples was measured at 25.1 and 50.3 MHZ, and the spin-lattice relaxation time of all the samples was measured at 50.3 MHZ. The NMR data indicate that the local motion of the ribose carbons is much less restricted than that of the bases for DNA and tRNA. The local motion correlation times of the ribose carbons are in the range of 1-7 ns for the samples investigated. The local motion correlation times of the different nucleic acids are quite similar with the exception that the 2' carbon of DNA and poly(A) is apparently less restricted than that for tRNA. The local motion correlation times of the ribose carbons, except perhaps the 2', do not appear to be strongly coupled to the conformation of the polynucleotide. The 13C NMR results can be combined with those of other investigations to obtain a consistent picture of the internal and overall motions of polynucleotides which have a backbone that is much more flexible than that of the bases.