A cleavage reagent directed to the active site of the Tetrahymena catalytic RNA was synthesized by derivatization of the guanosine substrate with a metal chelator. When complexed with iron(II), this reagent cleaved the RNA in five regions. Cleavage at adenosine 207, which is far from the guanosine-binding site in the primary and secondary structure, provides a constraint for the higher order folding of the RNA. This cleavage site constitutes physical evidence for a key feature of the Michel-Westhof model. Targeting a reactive entity to a specific site should be generally useful for determining proximity within folded RNA molecules or ribonucleoprotein complexes.