Mitochondria are essential constituents of eukaryotic cells, and their numerous functions include cellular respiration and generation of ATP. To maintain these mitochondrial functions, it is crucial to secure protein homeostasis, i.e. maintenance of a functional protein population. This task is executed through a sophisticated protein quality control network of molecular chaperones and proteases. In particular, the generation of reactive oxygen species at respiratory chain complexes is a major threat to the integrity of the organelle. This requires the removal of damaged proteins by the Pim1/Lon protease. As components of the protein quality control machinery are encoded by nuclear genes, mitochondrial stress conditions need to be signaled to the nucleus, a process that requires the action of another mitochondrial protease, ClpP.
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