title: Nascent polypeptide-associated complex stimulates protein import into yeast mitochondria.
abstract: To identify yeast cytosolic proteins that mediate targeting of precursor proteins to mitochondria, we developed an in vitro import system consisting of purified yeast mitochondria and a radiolabeled mitochondrial precursor protein whose C terminus was still attached to the ribosome. In this system, the N terminus of the nascent chain was translocated across both mitochondrial membranes, generating a translocation intermediate spanning both membranes. The nascent chain could then be completely chased into the mitochondrial matrix after release from the ribosome. Generation of this import intermediate was dependent on a mitochondrial membrane potential, mitochondrial surface proteins, and was stimulated by proteins that could be released from the ribosomes by high salt. The major salt-released stimulatory factor was yeast nascent polypeptide-associated complex (NAC). Purified NAC fully restored import of salt-washed ribosome-bound nascent chains by enhancing productive binding of the chains to mitochondria. We propose that ribosome-associated NAC facilitates recognition of nascent precursor chains by the mitochondrial import machinery.
authors.affiliation: Biozentrum der Universität Basel, CH-4055 Basel, Switzerland.
authors.forename: U
authors.initials: U
authors.lastname: Fünfschilling
authors.forename: S
authors.initials: S
authors.lastname: Rospert
mesh_terms: D001692:Biological Transport; D003600:Cytosol / Q000378:metabolism; D005656:Fungal Proteins / Q000378:metabolism*; D007425:Intracellular Membranes / Q000378:metabolism; D008666:Metalloendopeptidases / Q000235:genetics / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism*; D018832:Molecular Chaperones; D011499:Protein Processing, Post-Translational; D012270:Ribosomes / Q000378:metabolism; D015534:Trans-Activators / Q000737:chemistry / Q000494:pharmacology*; D015003:Yeasts / Q000378:metabolism*; D000096122:Mitochondrial Processing Peptidase
chemical_list: D005656:Fungal Proteins; D008666:Metalloendopeptidases; D018832:Molecular Chaperones; D015534:Trans-Activators; D000096122:Mitochondrial Processing Peptidase; C096099:nascent-polypeptide-associated complex