Defining the inside and outside of a catalytic RNA molecule.

Ribozymes are RNA molecules that catalyze biochemical reactions. Fe(II)-EDTA, a solvent-based reagent which cleaves both double- and single-stranded RNA, was used to investigate the structure of the Tetrahymena ribozyme. Regions of cleavage alternate with regions of substantial protection along the entire RNA molecule. In particular, most of the catalytic core shows greatly reduced cleavage. These data constitute experimental evidence that an RNA enzyme, like a protein enzyme, has an interior and an exterior. Determination of positions where the phosphodiester backbone of the RNA is on the inside or on the outside of the molecule provides major constraints for modeling the three-dimensional structure of the Tetrahymena ribozyme. This approach should be generally informative for structured RNA molecules.