Site-directed spin labelling of nucleic acids

The study of the structure and dynamics of the nucleic acids and their complexes with other biomolecules is the basis for understanding their functions. Electron paramagnetic resonance (EPR) spectroscopy is a biophysical technique that in recent years has been increasingly used to investigate nucleic acids. EPR studies require paramagnetic centre(s), usually nitroxide spin-label(s) that are incorporated at specific sites in the nucleic acid by site-directed spin labelling (SDSL). In the last few years, spin labels with improved spectroscopic properties have emerged and new SDSL techniques have been developed. This microreview describes SDSL of nucleic acids in the context of the three spin labelling strategies: post-synthetic spin labelling, labelling during oligonucleotide synthesis and noncovalent labelling. The application of EPR spectroscopy to study of the structures and dynamics of nucleic acids requires site-specific incorporation of stable free radicals (spin labels), known as site-directed spin labelling (SDSL). This review recapitulates the three main strategies used for SDSL of nucleic acids: spin labelling during oligonucleotide synthesis, post-synthetic labelling and noncovalent labelling.