Differential translation of the Na,K-ATPase subunit mRNAs

Expression of the Na,K-ATPase alpha and beta subunit genes is influenced by a complex series of regulatory pathways. For example, unequal amounts of subunit mRNAs are detected in several tissues, both at rest and upon mRNA induction, even though equal quantities of subunit proteins exist. We therefore studied mRNA stability and translational efficiency of wild type, deletion mutant, and chimeric subunit mRNAs in a cell-free translation system, to examine the possible role of post-transcriptional events in regulating subunit expression. alpha 1 mRNA translated less efficiently than beta 1 mRNA and competed less efficiently for rate-limiting translation factors. Deletion of the 5'-untranslated region of alpha 1 mRNA significantly increased its translation efficiency. Conversely, the alpha 1 5'-untranslated region impaired translation of beta 1 mRNA when attached upstream of the beta 1 coding sequence. This region is G/C-rich, and has a complex mRNA secondary structure. We propose that differential translational efficiency may contribute to the equal biosynthesis of subunit proteins in those tissues in which subunit mRNAs either exist in unequal amounts or are differentially induced.