3'-Untranslated regions of oxidative phosphorylation mRNAs function in vivo, as enhancers of translation

Recent findings have indicated that the 3'-untranslated region (3'-UTR) of the mRNA encoding the β-catalytic subunit of the mitochondrial H+-ATP synthase has an in vitro translationenhancing activity (TEA) [Izquierdo and Cuezva, Mol. Cell. Biol. (1997) 17, 5255-5268; Izquierdo and Cuezva, Biochem. J. (2000) 346, 849-855]. In the present work, we have expressed chimaeric plasmids that encode mRNA variants of green fluorescent protein in normal rat kidney and liver clone 9 cells to determine whether the 3'-UTRs of nuclear-encoded mRNAs involved in the biogenesis of mitochondria have an intrinsic TEA. TEA is found in the 3'-UTR of the mRNAs encoding the α- and β-subunits of the rat H+-ATP synthase complex, as well as in subunit IV of cytochrome c oxidase. No TEA is present in the 3'-UTR of the somatic mRNA encoding rat mitochondrial transcription factor A. Interestingly, the TEA of the 3'-UTR of mRNAs of oxidative phosphorylation is different, depending upon the cell type analysed. These data provide the first in vivo evidence of a novel cell-specific mechanism for the control of the translation of mRNAs required in mitochondrial function.