Figure 1.

Tetrahymena group I intron secondary structure. This schematic diagram of the intron illustrates the secondary structure of the L-21 G414 version of the Tetrahymena group I self-splicing intron with a substrate oligonucleotide bound to the internal guide sequence (IGS). Heavy lines and letters indicate nucleic acid sequences while thin arrows trace the connections between sequence elements. Important paired (P) and joining (J) regions are labeled. Interacting nucleotides C(-5), G26, U300, A97, and U277 are marked with circles, and the mutations examined in this work are indicated. Individual nucleotides in regions P2-P2.1, P5abc, and P9-P9.2 have been omitted for clarity but are present in the RNAs characterized in this study.