Yeast mitochondrial biogenesis: A role for the PUF RNA-binding protein puf3p in mRNA localization

Abstract

The asymmetric localization of mRNA plays an important role in coordinating posttranscriptional events in eukaryotic cells. We investigated the peripheral mitochodrial localization of nuclear-encoded mRNAS (MLR) in various conditions in which the MRNA binding protein context and the translation efficiency were altered. We identified Puf3p, a Pumilio family RNA-binding protein, as the first trans-acting factor controlling the MLR phenomenon. This allowed the characterization of two clases of genes whose mRNAs are translated to the vicinity of mitochondria. Class I mRNAs (256 genes) have a Puf3p binding motif in their 3′UTR region and many of them have their MLR properties deeply affected cy PUF3 deletion. Coversely, mutations in the Puf3p binding motif alter the mitochodrial localization of BCS1 mRNA. Class II mRNs (224 genes) have no Puf3p binding site and their asymmetric localization is not affected by the absense of PUF3. In agreement with a co-translational import process, we observed that the presence of puromysin loosens the interactions between most of the MLR-mRNAs and mitochodria. Unexpectedly, cycloheximide, suppposed to solidify translational complexe, turned out to destabilize a class of mRNA-mitochodria interactions. Classes I and II mRNAs, which are therfore transported to the motochondria through different pathways, correlated with different functional modules. Indeed, Class I genes code pricipally for the assembly factors of respiratory chain complexes and the mitochodrial translation machinery (ribosomes and thranslation regulators). Class II genes encode proteins of the respiratory chain or proteins involved in metabolic pathways. Thus, MLR, which is intimately linked to translation control, and the activity of mRNA-binding proteins like Puf3p, may provide the conditions for a fine spatiotemporal control of mitochondrial protein import and mitochondrial protein complex assembly. This work therefore provides new openings for the global study of mitochondria biogenesis. © 2008 Saint-Georges et al.