Targeting of cytosolic mRNA to mitochondria: Naked RNA can bind to the mitochondrial surface

Mitochondria contain hundreds of proteins but only a few are encoded by the mitochondrial genome. The other proteins are nuclear-encoded and imported into mitochondria. These proteins can be translated on free cytosolic polysomes, then targeted and imported into mitochondria. Nonetheless, numerous cytosolic mRNAs encoding mitochondria] proteins are detected at the surface of mitochondria in yeast, plants and animals. The localization of mRNAs to the vicinity of mitochondria would be a way for mitochondria] protein sorting. The mechanisms responsible for mRNA targeting to mitochondria are not clearly identified. Sequences within the mRNA molecules (cis-elements), as well as a few trans-acting factors, have been shown to be essential for targeting of some mRNAs. In order to identify receptors involved in mRNA docking to the mitochondrial surface, we have developed an in vitro mRNA binding assay with isolated plant mitochondria. We show that naked mRNAs are able to bind to isolated mitochondria, and our results strongly suggest that mRNA docking to the plant mitochondria] outer membrane requires at least one component of TOM complex. (C) 2013 Elsevier Masson SAS. All rights reserved.