Mitochondrial precursor proteins are directed into the intermembrane space via two different routes, the presequence pathway and the redox-dependent MIA pathway. The pathways were assumed to be independent and transport different proteins. We report that the intermembrane space receptor Mia40 can switch between both pathways. In fungi, Mia40 is synthesized as large protein with an N-terminal presequence, whereas in metazoans and plants, Mia40 consists only of the conserved C-terminal domain. Human MIA40 and the C-terminal domain of yeast Mia40 (termed Mia40core) rescued the viability of Mia40-deficient yeast independently of the presence of a presequence. Purified Mia40core was imported into mitochondria via the MIA pathway. With cells expressing both full-length Mia40 and Mia40core, we demonstrate that yeast Mia40 contains dual targeting information, directing the large precursor onto the presequence pathway and the smaller Mia40core onto the MIA pathway, raising interesting implications for the evolution of mitochondrial protein sorting
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