Efficient enzymatic synthesis of C-13,N-15-labeled DNA for NMR studies

The power of heteronuclear NMR spectroscopy to study macromolecules and their complexes has been amply demonstrated over the last decade. The obstacle to routinely applying these techniques to the study of DNA has been the synthesis of C-13, N-15-labeled DNA. Here we present a simple and efficient method to generate isotope-labeled DNA for NMR studies that is as easy as that for isotope labeling of RNA. The method was used to synthesize a uniformly C-13, N-15-labeled 32-nucleotide DNA that binds to human basic fibroblast growth factor with high affinity and specificity. Isotope-edited experiments were applied to the C-13, N-15-labeled DNA bound to unlabeled protein, and the C-13, N-15-labeled DNA was also examined in complex with N-15-labeled protein. The NMR experiments show that the DNA adopts a well-defined stable structure when bound to the protein, and illustrate the potential of C-13, N-15-labeled DNA for structural studies of DNA-protein complexes.