Assembly of mitochondria in yeast. Complementation of mitochondrial and cytosolic products in a temporal sequence in vitro

Mitochondrial translation products during release from glucose repression in Saccharomyces cerevisiae

Mitochondrial protein synthesis was studied during release from glucose repression in Saccharomyces cerevisiae cells bearing different mitochondrial genomes. The increase in the rate of the synthesis of mitochondrial translation products was analyzed during respiratory induction. Different kinetic patterns were found for strains having a different structure of mitochondrial mosaic genes, even when the nuclear background was the same. A very limited response of the synthesis of the var1 ribosomal protein to inducing conditions was observed.

Does more than one mitochondrially synthesized protein in yeast have larger precursors?

Yeast cells undergoing derepression (the phase of mitochondriogenesis) were exposed to [14C]formate in the presence of cycloheximide, the cytosolic protein synthesis inhibitor, and of 1,10-phenanthroline, a metallo-protease inhibitor. Extensive labelling was obtained under such conditions. Incubation of these labelled products with mitochondrial lysates released small peptides (mol. wt. 500-1000). These results indicate that mitochondria probably synthesize some of the proteins in the precursor form and they are processed by a specific matrix-located protease before proper integration.

Synthesis and assembly of cytochrome c oxidase in synchronous cultures of yeast

Yeast cells growing synchronously in glucose medium accumulate in the cytosol, the cytosolically made subunits of cytochrome oxidase, during the G1 and early-S phases. The mitochondrially made subunits, on the other hand, are detected only after the mid-S phase. The cytosolically synthesized subunits are integrated into the membrane after the mid-S phase.

Synthesis and assembly of adenosinetriphosphatase in synchronous cultures of yeast

Maximal respiration and expression of mitochondrial enzymes are found at the late-S phase of yeast cells growing synchronously in glucose medium. Adenosinetriphosphatase (ATPase) activity follows a similar pattern. However, the cytosolically synthesized F1-ATPase and also that released from the membrane accumulate in the cytosol during the G1 and early-S phases. After the mid-S phase, when the mitochondrially synthesized membrane factors are available, the enzyme migrates to the membrane and is integrated.