Mitochondria import 99% of their proteome as precursor proteins from the cytosol. We are investigating the pathways these precursors take from their synthesis on cytosolic ribosomes to their final destination within the mitochondria. In particular, we focus on the maturation process by proteolytic removal of the targeting signals, which is carried out by highly conserved presequence proteases and essential for the generation and maintenance of a functional mitochondrial proteome.