2-aminopurine as a probe of RNA conformational transitions.

2-aminopurine (2AP) is a fluorescent nucleobase that provides the means to probe structure and dynamics of RNA molecules. Because 2AP can base pair with Uridine, it can replace normal A:U pairs without substantial deformation of duplexes. It is best used as a probe of ostensibly single-stranded regions: its fluorescence intensity reports on base stacking and its fluorescence decay lifetimes report on its conformational dynamics. Three examples of its use are described here, illustrating how 2AP fluorescence has been used to probe RNA folding and hairpin loop dynamics.