A conserved base pair within helix P4 of the Tetrahymena ribozyme helps to form the tertiary structure required for self-splicing.
Flor PJ, Flanegan JB, Cech TR. A conserved base pair within helix P4 of the Tetrahymena ribozyme helps to form the tertiary structure required for self-splicing. EMBO J. 1989 Nov; 8(11):3391-9.