SELECTION OF NOVEL MG2-DEPENDENT SELF-CLEAVING RIBOZYMES()

Four RNA motifs are known that catalyse site-specific cleavage in the presence of Mg2+ ions, all discovered in natural RNAs. In a single in vitro selection experiment we have isolated representatives of five no vel classes of Mg2+-dependent ribozymes. Small versions of three of th ese showed that a very simple internal loop type of secondary structur e is responsible for the activity. One of these was synthesized in a b imolecular form, and compared directly with the hammerhead ribozyme; f or the new ribozyme, the cleavage step of the reaction is much faster than the spontaneous rate of phosphodiester bond cleavage, yet substan tially slower than that for the hammerhead. The results suggest that m any more Mg2+-dependent self-cleaving RNA sequences can be found.