Suppression of mutations in the core of the Tetrahymena ribozyme by spermidine, ethanol and by substrate stabilization.

We have previously described a collection of mutations in conserved residues of the core of the Tetrahymena self-splicing intron. Most of these single base substitutions have less than 10% of the activity of their parental intron derivative [Couture, S., et al., (1990) J. Mol. Biol., 215, 345-358]. We examined the effect of two agents known to stabilize RNA structure, spermidine and ethanol, on the activity of many of these mutant RNAs. In the presence of either 5 mM spermidine or 20% ethanol most substitution mutations were partially or completely suppressed. These conditions also increased the temperature optima of both wild-type and mutant ribozymes. In addition, we find that mutations are also suppressed by a high concentration of GTP, a substrate in the reaction which is bound specifically by the intron. Thus we observe a general suppression of mutations in an RNA enzyme (ribozyme) by spermidine, ethanol and by substrate stabilization. These results are consistent with the idea that most mutations destabilize the folded structure of the ribozyme and can be suppressed by any of a variety of stabilizing influences.