Differential effects of translational inhibition in cis and in trans on the decay of the unstable yeast MFA2 mRNA.

Several observations in eukaryotic cells suggest that the processes of translation and mRNA turnover are interrelated. To understand this relationship, we examined the effects of translational inhibition on the decay of the unstable yeast MFA2 mRNA, which is degraded in a 5' to 3' direction following deadenylation (1). Although inhibition of translation in cis stabilizes several unstable mammalian transcripts, inhibiting translation of the MFA2 mRNA in cis, by the insertion of a large stem-loop structure in the 5'-untranslated region (UTR), did not affect the half-life, deadenylation rate, or appearance of specific decay intermediates. Therefore, efficient translational elongation on the MFA2 mRNA is not a requirement for the normal rate, or mechanism, of degradation of this transcript. In contrast, inhibition of translation in trans, by the addition of cycloheximide, stabilized the deadenylated form of MFA2 mRNA. Furthermore, the MFA2 transcripts that were not translated due to a stem-loop in the 5'-UTR were also stabilized in the presence of cycloheximide, suggesting that cycloheximide is likely to affect mRNA stability indirectly. These results suggest possible relationships between the mechanisms of mRNA decay and the translational process.