Assembly of the Mitochondrial Membrane System

Abstract Mitochondrial particles prepared from glucose-repressed yeast bind only nominal amounts of the soluble ATPase components, rutamycin-insensitive ATPase and oligomycin sensitivity-conferring protein, when tested in an in vitro reconstitution assay. The capacity of the membranes to bind these components and to reconstitute rutamycin-sensitive ATPase increases when the cells are incubated in a derepression medium, suggesting that a membrane factor essential for the reconstitution is synthesized during the derepression. The effect of inhibitors of protein synthesis on the increase of the membrane factor during derepression has been studied. The membrane factor does not increase when either chloramphenicol or cycloheximide is added to the derepression medium. Increase of membrane factor, however, is found when yeast are incubated sequentially in derepression media containing first chloramphenicol and then cycloheximide. These results have been interpreted to indicate that the membrane factor is made by the mitochondrial protein-synthesizing system and that its synthesis is stimulated by products of the cytoplasmic ribosomal protein-synthesizing system. A positive control of mitochondrial protein synthesis by products of cytoplasmic ribosomal system is also supported by studies on the in vivo incorporation of amino acids into mitochondrial membrane proteins.