... of the 5¢ exon, and 25 bp of the 3¢ exon. Oligo 104 (45 nucleotides, TAATACGACTCACTATAGGGATCGAATTCTGGGTTCAAAACGTAA)contains, in order, a T7 RNA polymerase promoter (nucleo-tides 1–17), a six-nucleotide ... transcription enhancer, anEcoRI restriction site, 14 nucleotides of authentic 5¢ exon,and the first two nucleotides of the Cr.LSU intron. Oligo 158(26 nucleotides, GAAATT TTAAAGCCGAATAAAACTTG)ends ... especially the intron from the large rRNA gene of Tetrahymena thermophila(Tt.LSU), indicate that some domains are modular,and that the catalytic site is buried inside the foldedribozyme [5–7]. The...