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 form of a trans-acting delta ribozyme. A specific Mg(2+)-induced cleavage at position G(52)at the bottom of the P2 stem was observed to occur solely within catalytically active ribozyme-substrate complexes (i.e. those that performed the essential conformational transition step). Only the divalent cations which support catalytic activity permitted the detection of specific induced cleavages in this region. Using various mutant ribozymes and substrates, we demonstrated a correlation between enzymatic activity and the Mg(2+)-induced 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 pair 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 of a structural rearrangement involving the bottom of the P2 stem upon formation of the P1 helix, these results show that an intimate relationship exists between the folding and the catalytic activity of the delta ribozyme.