title: Coupling of protein synthesis and mitochondrial import in a homologous yeast in vitro system.
abstract: We made use of a homologous cell-free mitochondrial protein import system derived from the yeast Saccharomyces cerevisiae to investigate the coupling of protein synthesis and import. Mitochondrial precursor proteins were synthesized in a yeast lysate either in the presence or absence of isolated yeast mitochondria. We were, therefore, able to analyze protein import into mitochondria either in a strictly posttranslational reaction (when isolated mitochondria were added only after protein synthesis has been arrested by the addition of cycloheximide) or in a reaction in which synthesis and import were permitted to occur simultaneously. We found that the import of a precursor protein consisting of the amino-terminal mitochondrial targeting sequence of cytochrome oxidase subunit IV fused to mouse dihydrofolate reductase is very inefficient in a strictly posttranslational reaction, whereas efficient import is observed if precursor synthesis and import are coupled. The same result was obtained when we analyzed the import of bulk endogenous yeast mitochondrial proteins in this system. Finally, we found that the insertion of the yeast outer membrane protein porin is also several times more efficient when synthesis and insertion are coupled.
authors.affiliation: Department of Cellular and Molecular Physiology, Milton S. Hershey Medical Center, Pennsylvania State University, Hershey 17033.
authors.forename: M
authors.initials: M
authors.lastname: Fujiki
authors.forename: K
authors.initials: K
authors.lastname: Verner
mesh_terms: D000818:Animals; D001425:Bacterial Outer Membrane Proteins / Q000096:biosynthesis / Q000235:genetics; D002474:Cell-Free System; D003513:Cycloheximide / Q000494:pharmacology; D003576:Electron Transport Complex IV / Q000096:biosynthesis / Q000235:genetics; D005656:Fungal Proteins / Q000096:biosynthesis* / Q000235:genetics; D007700:Kinetics; D046911:Macromolecular Substances; D051379:Mice; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D018272:Porins; D011499:Protein Processing, Post-Translational; D011691:Puromycin / Q000494:pharmacology; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D013762:Tetrahydrofolate Dehydrogenase / Q000096:biosynthesis / Q000235:genetics
chemical_list: D001425:Bacterial Outer Membrane Proteins; D005656:Fungal Proteins; D046911:Macromolecular Substances; D018272:Porins; D011993:Recombinant Fusion Proteins; D011691:Puromycin; D003513:Cycloheximide; D013762:Tetrahydrofolate Dehydrogenase; D003576:Electron Transport Complex IV