Till recently, hydroxyl radical probing was the method for  measuring RNA-nucleobase solvent accessibility, but it requires  synchrotron radiation, and thus is challenging to apply in vitro. Feng et al.  now present light-activated structural examination of RNA (LASER), a  synchrotron-free alternative method for probing the solvent  accessibility of purine nucleobases. The approach uses nicotinoyl azide,  which, when hit with light, undergoes a rapid chemical reaction to form  adducts with solvent-exposed guanosines and adenosines on a folded RNA.  Such tagged sites are detected by reverse transcription of the modified  RNA followed by denaturing gel electrophoresis. The method detects  rapid changes in RNA structure after ligand binding and yields results  very similar to those obtained by hydroxyl radical probing, but it works  both outside and inside cells.

Source - https://doi.org/10.1038/nchembio.2548