Regulation of mitochondrial protein synthesis by cytoplasmic proteins.

Abstract

Isolated yeast [Saccharomyces cerevisiae] mitochondria, which synthesize identifiable polypeptides identical to those made in vivo, were used in an in vitro system to study cytoplasmic control of mitochondrial protein synthesis. It was found that protein synthesis in isolated mitochondria is dependent on an endogenous pool of cytoplasmically synthesized proteins present within mitochondria at the time of isolation, that protein synthesis ceases apparently when this pool of proteins is depleted, and that a cytoplasmic extract can restore protein synthesis in depleted mitochondria. By use of depleted mitochondria to assay for stimulatory factors it was found that the bulk of the stimulatory activity in the cytoplasm is of a protein nature and resides predominantly in the postpolysomal supernatant. At least 1 cytoplasmic stimulatory protein appears to exert a specific effect on the synthesis of subunits I-III of cytochrome c oxidase (ferrocytochrome c:oxygen oxidoreductase; EC 1.9.3.1).