The eukaryotic family of RNA-binding proteins termed PUF (Pumilio and FBF) is known for its roles in cell division, differentiation and development. The best-characterized function of PUFs is as posttranscriptional repressors. Recent studies have indicated that PUFs can also activate gene expression. Moreover, it is becoming clear that PUFs facilitate mRNA localization for spatial control of expression. Here, we review the emerging concept of PUF proteins as versatile posttranscriptional regulators. We discuss how the functions of PUFs as repressors and mRNA targeting factors could be integrated by focusing on Puf3 and Puf6 from yeast and propose a model for how the roles of Puf3 in mRNA targeting to the mitochondria and mRNA repression might promote cotranslational import into mitochondria and mitochondrial biogenesis.
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