Influence of the 5'-end region of aldehyde dehydrogenase mRNA on translational efficiency. Potential secondary structure inhibition of translation in vitro.

mRNA coding for rat liver mitochondrial aldehyde dehydrogenase was translated in rabbit reticulocytes 10 times more efficiently than was the corresponding bovine mRNA. Previous data showed that the mRNAs primarily differed in the noncoding 5'-end (K.-L. Guan and H. Weiner, manuscript submitted for publication to Arch. Biochem. Biophys.). Fusion mRNAs were constructed so that the 5'-untranslated region from one was attached to the coding sequence of the other. Furthermore, the mRNAs were mutated at position -3, a position implicated in translational regulation, so that both contained the same residues. Results indicated that the dramatic difference in translational rates between rat and bovine mRNAs was just partly due to the sequence around the initiation codon. Secondary structure prediction of mRNA indicated that stable secondary structure could exist in the 5'-end of bovine mRNA, whereas no such stable structure should exist in rat mRNA. Existence of the predicted secondary structure of bovine mRNA was substantiated by the observation that termination in DNA sequencing in the 5'-end of bovine cDNA occurred. It is concluded that stable secondary structure in the 5'-end region of bovine mitochondrial aldehyde dehydrogenase performs a major role in inhibiting translation. This inhibitory effect is related to the magnitude of free energy required to melt the secondary structure in order to reach the initiation AUG codon.