![]() ![]() It is widely accepted that, after being translated by cytosolic ribosomes, mitochondrial proteins are post-translationally directed to the translocase of the outer membrane (TOM) complex, the entrance gate at the mitochondria. Hence, one of the most challenging events during the biogenesis of nuclear-encoded mitochondrial proteins is their proper sorting to the mitochondrial surface to achieve their transport inside the organelle ( 5, 6). During evolution, most mitochondrial genes have been transferred to the nucleus ( 4). As a result of their endosymbiotic origin ( 1, 2), the mitochondrial proteome is encoded in both the nuclear and the mitochondrial genomes ( 3). Mitochondria are one of the most important organelles in eukaryotic cells because of the vital functions that occur within their membranes. Furthermore, we explored the presence of this cluster at the N terminus of the mitochondrial proteome and propose a set of precursors whose proper localization depends on both αβ′-NAC and Sam37. Our results reveal the presence of a positively charged amino acid cluster in the MTS of select mitochondrial precursors, such as Oxa1 and Fum1, which are crucial for their recognition by αβ′-NAC. We used targeting signals of different mitochondrial proteins (αβ′-NAC-dependent Oxa1 and αβ′-NAC-independent Mdm38) and fused them to GFP to study their intracellular localization by biochemical and microscopy methods, and in addition followed their import kinetics in vivo. In this work, we aimed to detect the region in the MTS of mitochondrial precursors relevant for their recognition by αβ′-NAC during their sorting to the mitochondria. ![]() We have previously described that the mitochondrial outer membrane protein Sam37 interacts with αβ′-NAC and together promote the import of specific mitochondrial precursor proteins. ![]() The cytosolic chaperone nascent polypeptide–associated complex (NAC), which in yeast is represented as the two different heterodimers αβ-NAC and αβ′-NAC, has been proposed to be involved during the early steps of mitochondrial protein targeting. However, the early steps of mitochondrial protein targeting remain undeciphered. For a subset of mitochondrial proteins, a signal sequence at the N terminus (matrix-targeting sequence ) is recognized by protein complexes to ensure their proper translocation into the organelle. A major challenge in eukaryotic cells is the proper distribution of nuclear-encoded proteins to the correct organelles. ![]()
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