Formation of yeast mitochondria. 3. Biochemical properties of mitochondria isolated from a cytoplasmic petite mutant

Mitochondrial mutations may increase oxidative stress: implications for carcinogenesis and aging?

The sensitivity of mitochondrial DNA to damage by mutagens predisposes mitochondria to injury on exposure of cells to genotoxins or oxidative stress. Damage to the mitochondrial genome causing mutations or loss of mitochondrial gene products, or to some nuclear genes encoding mitochondrial membrane proteins, may accelerate release of reactive species of oxygen. Such aberrant mitochondria may contribute to cellular aging and promotion of cancer.

Integration and regulation of mitochondrial assembly in yeast

The interactions between the mitochondrial and nucleocytoplasmic systems required for mitochondriogenesis have been investigated at several different levels. Those involved in the formation of functional enzyme complexes have been studied using cytochrome oxidase: this multimeric (2 X 7 and 2 X 6 subunits for enzymes from yeast and beef heart respectively) has been resolved, and the mitochondrial contribution has been shown to be dispensible for catalytic function proper. Using novel mutants, with a mitochondrial mode of inheritance, a mitochondrial gene product localized in the oligomycin-sensitive ATPase has been implicated in the assembly not only of this complex, but of cytochrome oxidase as well. Interactions required for the genetic competence of the mitochondrial system have become apparent as a result of studies in the mechanism of action of the highly effective mitochondrial mutagen ethidium bromide. This agent first becomes covalently inserted into mitochondrial DNA and, after its excision, eventually results in extensive degradation of the macromolecule. The excision reaction has now been shown to be performed by a complex between the oligomycin-sensitive ATPase and a DNA-binding protein presumably involved in recognizing the damage. On the level of replication and expression of the mitochondrial genome studies using thermolabile mutants have demonstrated that these processes appear independent of the replication of nuclear DNA but not of its expression.

Biogenesis of mitochondria. The effects of physiological and genetic manipulation of Saccharomyces cerevisiae on the mitochondrial transport systems for tricarboxylate-cycle anions

1. Kinetic and equilibrium parameters for the uptake of l-malate, succinate, citrate and alpha-oxoglutarate by fully functional mitochondria of Saccharomyces cerevisiae were determined. 2. The uptake of l-malate and succinate is mediated by a common carrier, and two other distinct carriers mediate the uptake of citrate and alpha-oxoglutarate. 3. The properties of the carrier systems for l-malate, succinate and citrate closely resemble those of mammalian mitochondria, but the alpha-oxoglutarate carrier differs from the mammalian system in minor respects. 4. The composition of the yeast mitochondria was extensively manipulated by (a) anaerobiosis, (b) catabolite repression, (c) inhibition of mitochondrial protein synthesis and (d) elimination of mitochondrial DNA by mutation. 5. The carrier systems for l-malate, succinate, citrate and alpha-oxoglutarate are essentially similar in the five different types of mitochondria. 6. It is concluded that all the protein components of the carrier systems for l-malate, succinate, citrate and alpha-oxoglutarate are coded by nuclear genes and synthesized extramitochondrially by cell-sap ribosomes.

Expression of the mitochondrial genome in HeLa cells. IX. Effect of inhibition of mitochondrial protein synthesis on mitochondrial formation

The effect of selective inhibition of mitochondrial protein synthesis by chloramphenicol at 40 or 200 microg/ml on the formation of mitochondria in HeLa cells was investigated. HeLa cells, under the conditions used in the present work, grow at a decreasing rate for at least four cell generations in the presence of 40 microg/ml chloramphenicol, and for two generations in the presence of 200 microg/ml chloramphenicol. The progressive cell growth inhibition which begins after 2 days of exposure of the cells to 40 microg/ml chloramphenicol is immediately or gradually reversible, upon removal of the drug, for periods up to at least 8 days of treatment, though there is a progressive loss of cloning efficiency. In cells which have been treated for 6-7 days with 40 or 200 microg/ml of chloramphenicol, mitochondrial protein synthesis occurs at a normal or near-normal rate 1 h after removal of the drug. Mitochondria increase normally in number and show a normal size and amount of cristae in the presence of either concentration of drug. However, in 4-5% of the mitochondrial profiles the cristae appear to be arranged in unusual, circular, looped or whorled configuration.