FIG. 1.
Mutations examined in this study. (A) Schematic diagram of SL2 RNA with point mutations. Phylogenetically perfectly conserved positions are shaded (14). The stem-loops are labeled (I, II, and III) as discussed in the text. The arrow marks the site of trans splicing. Point mutations are indicated. The Sm binding site consensus sequence is RAU4–6GR (reviewed in reference 42). (B) Large substitution mutations (boxed) are shown next to the wild-type SL2 RNA structure. Nucleotide positions marked with an asterisk remain unchanged in the mutated SL2 RNA. (C) PSE mutation. The sequences shown are the consensus C. elegans PSE and the proposed PSE from the SL2α gene (53). Invariant positions are indicated by dots (53). The 5′ end of the PSE in this gene is 65 bp upstream of the transcription start site (53). The mutated sequence tested is boxed.