| Abstract
| - Hammerhead ribozymes (Rz) have catalytically important tandem G:A pairs in the core region,and we recently demonstrated that the P9-G10.1 motif (a sheared-type G:A pair with a guanine residue onthe 3‘ side of the adenine residue) with several flanking base pairs is sufficient for capture of divalentcations, such as Mg2+ and Cd2+ ions that are important to maintain full activities (Tanaka et al. J.Am.Chem.Soc.2002, 124, 4595−4601; Tanaka et al. J.Am.Chem.Soc.2004, 126, 744−752). We alsofound that mutant hammerhead ribozymes that have an additional G residue inserted between A9 andG10.1 residues (the metal-binding P9-G10.1 motif) have significant catalytic activities. In this study, wedemonstrate that the hammerhead ribozymes are capable of maintaining the catalytically competent structureeven when the tandem, sheared-type G:A pairs were perturbed by an insertion of an additional nucleotide,whereas the chirality of the phosphorothioate at the P9 position significantly influenced the enzymatic activityfor both the natural and G-inserted ribozymes.
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