Uses of ¹³C- and ¹⁵N-labeled RNA in NMR of RNA-protein complexes

The interactions between RNA and protein will not be simple ones in the sense that they cannot be predicted by the structure of the free RNA. The assumption in describing these interactions must be that the RNA nucleotide is free to use any or all of its chemical moieties to anchor it to the protein, and the spectroscopist must be ready for these possibilities. The incorporation of both 15N and 13C into the RNA is absolutely necessary to obtain a picture of how the RNA is associated to the protein, and the implementation of pulsed field gradients allows observation of the critical hydrogen bonding sites. We must note here that since some of the hydrogen bonds between RNA and protein are certain to be mediated by water molecules, gradients should also provide a means to look for these specific associations.