Alteration of substrate specificity for the endoribonucleolytic cleavage of RNA by the Tetrahymena ribozyme.

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Abstract
A shortened form of the intervening sequence of the self-splicing RNA from Tetrahymena thermophila catalyzes sequence-specific cleavage of RNA. Cleavage site selection involves a base-pairing interaction between the substrate RNA and a binding site within the intervening sequence. Single-base changes in the binding site were previously shown to alter substrate specificity in a predictable manner. To examine the generality with which substrate specificity can be altered, six variant catalytic RNAs (ribozymes) have been produced with two- or three-base changes in the active site. Each ribozyme cleaves its predicted substrate. The conditions required for good reactivity and for discrimination against cleavage at mismatched sites vary and were independently determined for each ribozyme.