Control of the translational efficiency of beta-F1-ATPase mRNA depends on the regulation of a protein that binds the 3' untranslated region of the mRNA.

The expression of the nucleus-encoded beta-F1-ATPase gene of oxidative phosphorylation is developmentally regulated in the liver at both the transcriptional and posttranscriptional levels. In this study we have analyzed the potential mechanisms that control the cytoplasmic expression of beta-F1-ATPase mRNA during liver development. Remarkably, a full-length 3' untranslated region (UTR) of the transcript is required for its efficient in vitro translation. When the 3' UTR of beta-F1-ATPase mRNA is placed downstream of a reporter construct, it functions as a translational enhancer. In vitro translation experiments with full-length beta-F1-ATPase mRNA and with a chimeric reporter construct containing the 3' UTR of beta-F1-ATPase mRNA suggested the existence of an inhibitor of beta-F1-ATPase mRNA translation in the fetal liver. Electrophoretic mobility shift assays and UV cross-linking experiments allowed the identification of an acutely regulated protein (3'betaFBP) of the liver that binds at the 3' UTR of beta-F1-ATPase mRNA. The developmental profile of 3'betaFBP parallels the reported changes in the translational efficiency of beta-F1-ATPase mRNA during development. Fractionation of fetal liver extracts revealed that the inhibitory activity of beta-F1-ATPase mRNA translation cofractionates with 3'-UTR band-shifting activity. Compared to other tissues of the adult rat, kidney and spleen extracts showed very high expression levels of 3'betaFBP. Translation of beta-F1-ATPase mRNA in the presence of kidney and spleen extracts further supported a translational inhibitory role for 3'betaFBP. Mapping experiments and a deletion mutant of the 3' UTR revealed that the cis-acting element for binding 3'betaFBP is located within a highly conserved region of the 3' UTR of mammalian beta-F1-ATPase mRNAs. Overall, we have identified a mechanism of translational control that regulates the rapid postnatal differentiation of liver mitochondria.