Roles of 2′-Hydroxyls of Leadzyme on an RNA Cleavage

The roles of two different 2′-hydroxyls near to a catalytic site of a leadzyme (Pb2+ ribozyme), CUGGGAGUCC, have been investigated kinetically. These roles of two different 2′-hydroxyls were clearly distinguished upon a cleavage reaction of an RNA substrate. One 2′-hydroxyl of G of the leadzyme in an asymmetry internal loop contributed to only the binding constant for the leadzyme with the substrates. The other 2′-hydroxyl of A in the asymmetry loop contributed to only the cleavage rate constant. On the basis of the results, we propose the possibility of the formation of a hydrogen bond between the 2′-hydroxyl of G of the leadzyme and the substrate and the binding between Pb2+ ion and the 2′-hydroxyl of A.