Presence of a coordinated metal ion in a trans-acting antigenomic delta ribozyme

We have investigated the cleavage induced by metal ions in an antigenomic f orm of a trans-acting delta ribozyme. A specific Mg2+-induced cleavage at p osition G(52) at the bottom of the P2 stem was observed to occur solely wit hin catalytically active ribozyme-substrate complexes (i.e. those that perf ormed the essential conformational transition step). Only the divalent cati ons which support catalytic activity permitted the detection of specific in duced cleavages in this region. Using various mutant ribozymes and substrat es, we demonstrated a correlation between enzymatic activity and the Mg2+-i nduced cleavage pattern. We show that the efficiency of the coordination of the magnesium to its binding site is related to the nature of the base pai r in the middle of the P1 stem (i.e. Rz(23-)S(8)). Together with additional evidence from nuclease probing experiments that indicates the occurrence o f a structural rearrangement involving the bottom of the P2 stem upon forma tion of the P1 helix, these results show that an intimate relationship exis ts between the folding and the catalytic activity of the delta ribozyme.