Imidazole Rescue of a Cytosine Mutation in a Self-Cleaving Ribozyme

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Science  01 Oct 1999:
Vol. 286, Issue 5437, pp. 123-126
DOI: 10.1126/science.286.5437.123

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Ribozymes use a number of the same catalytic strategies as protein enzymes. However, general base catalysis by a ribozyme has not been demonstrated. In the hepatitis delta virus antigenomic ribozyme, imidazole buffer rescued activity of a mutant with a cytosine-76 (C76) to uracil substitution. In addition, a C76 to adenine substitution reduced the apparent pK a (whereK a is the acid constant) of the self-cleavage reaction by an amount consistent with differences in the pK a values of these two side chains. These results suggest that, in the wild-type ribozyme, C76 acts as a general base. This finding has implications for potential catalytic functions of conserved cytosines and adenines in other ribozymes and in ribonuclear proteins with enzymatic activity.

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