A Study of Mitochondrial Protein Synthesis in Intact HeLa Cells

Abstract

Mitochondrial protein synthesis has been studied in intact HeLa cells by utilizing specific inhibitors. We have observed that in the presence of pederine, an inhibitor of cytoplasmic protein synthesis in mammalian cells, protein synthesis continues for at least 1 h at approximately 0.5% of the rate of untreated cells. When control cells and cells treated with pederine are fractionated after an incubation with labeled amino acids into a mitochondrial and a supernatant fraction, it is found that incorporation into the mitochondrial fraction is higher in the presence of the inhibitor. Mitochondrial protein synthesis has been shown to take place on aggregates of mitochondrial ribosomes.The synthesis of mitochondrial proteins has been studied by incubating HeLa cells with labeled amino acids and either pederine or chloramphenicol, an inhibitor of mitochondrial protein synthesis. We have been able to establish that the structural protein of mitochondrial ribosomes is synthesized on cytoplasmic ribosomes and its synthesis is thus inhibited by pederine, but not by chloramphenicol. Mitochondrial proteins have been analyzed by acrylamide gel electrophoresis after fractionation of the mitochondria into inner and outer membranes. Proteins synthesized by mitochondria in the presence of pederine are located predominantly on the inner mitochondrial membranes. Only few protein species synthesized by mitochondria are resolved by gel electrophoresis. This finding is discussed in relationship to the information content of mitochondrial DNA.