Catalytic activity is retained in theTetrahymenagroup I intron despite removal of the large extension of element P5

We have made sizeable internal deletions within the self-splicing group I intron of Tetrahymena thermophila. Deletions were made in a piecewise manner in order to remove secondary structural elements thought to be extraneous to the catalytic center of the molecule. The resulting deletion mutants retain self-splicing activity, albeit under modified reaction conditions that enhance duplex stability. Considering those portions of the molecule that can be deleted without a loss of catalytic activity, one is left with a catalytic center of approximately 130 nucleotides that is solely responsible for the molecule's activity.