Refolding of rRNA exons enhances dissociation of the Tetrahymena intron

Self-splicing of the Tetrahymena pre-rRNA is inhibited by a conserved rRNA hairpin P(-1) upstream of the 5' splice site. P(-1) inhibits self-splicing by competing with formation of the P1 splice site helix. Here we show that the P(-1) hairpin also enhances dissociation of the spliced products, which was monitored by native gel electrophoresis. Mutations that stabilize the rRNA hairpin increase the rate of dissociation approximately 10-fold, from 0.5 min^-1 for the wild-type RNA to ~4 min^-1 at 30°C. Conversely, mutations or oligonucleotides that inhibit refolding of the exons and that stabilize the P1 helix decrease the rate of product release. The results suggest that refolding of products can be used to stimulate the turnover of ribozyme-catalyzed reactions. In the pre-rRNA, this conformational change helps shift the equilibrium of self-splicing toward the mature rRNA.