Nascent polypeptide-associated complex stimulates protein import into yeast mitochondria.
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.
Fünfschilling
U
U
Biozentrum der Universität Basel, CH-4055 Basel, Switzerland.
Rospert
S
S
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
D005656:Fungal Proteins; D008666:Metalloendopeptidases; D018832:Molecular Chaperones; D015534:Trans-Activators; D000096122:Mitochondrial Processing Peptidase; C096099:nascent-polypeptide-associated complex