THE MITOCHONDRIAL GENETIC SYSTEM ....•••••• ••••••••••.• ••••••••••..•......... 291 Organization and Expression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . . . 291 Genetic Content 296 Regulation of Mitochondrial Gene Expression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300

Biogenesis of Mitochondria

Cytoplasmic inheritance and intragenomic conflict

The very high genome copy number in cytoplasmic organelles is a puzzling fact in cell biology. It is proposed here that high copy number reflects an increased need for organellar ribosomes that can only be satisfied by the increased ribosomal RNA gene number that results from genome multiplication.

Why do chloroplasts and mitochondria contain so many copies of their genome

Cytochrome c-oxidase (COX), the terminal enzyme of the mitochondrial respiratory chain, plays a key role in the regulation of aerobic production of energy. Biogenesis of eukaryotic COX involves the...

Assembly of mitochondrial cytochrome c-oxidase, a complicated and highly regulated cellular process

For what once were probably free-living aerobic bacteria, mitochondria show a surprising degree of domestication in terms of their dependence on the genetic system of the cells in which they reside. In most organisms, only a handful of the hundred or so mitochondrial proteins are encoded by mitochondrial DNA (mtDNA). The remainder, including most of the components of the mitochondrion’s own genetic system, are encoded by nuclear genes, which also specify all other enzymes necessary for the synthesis, import, processing and modification of these proteins and associated lipid components. The assembly of a functional mitochondrion is possibly one of the most complex logistic exercises faced by the eukaryotic cell. In a facultative anaerobic organism like the yeast Saccharomyces cerevisiae, which is capable of tailoring the level of mitochondrial biosynthesis to its specific needs in response to its environment, several hundred nuclear genes are likely to be involved in one way or another with mitochondrial biogenesis.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1989.tb14854.x

Nucleo-mitochondrial interactions in yeast mitochondrial biogenesis.

Genetic crosses were made using strains of Saccharomyces cerevisiae which carried cytoplasmically inherited markers conferring resistance to erythromycin, oligomycin and chloramphenicol. The frequency of transmission of these mitochondrial loci to diploid progeny was found to be influenced by the physiological state of the haploid parents, and was not affected by the cis or trans configuration of the three resistance markers. No recombinational polarity was seen in any of the crosses. Growth of a haploid parental strain to stationary phase in a yeast extract peptone medium containing glycerol as a carbon source resulted in a high level of transmission of mitochondrial markers when crossed with a strain grown to stationary phase in the same medium but with glucose as carbon source. When cells were grown under the same conditions as those used in the genetic crosses they were found to contain more mitochondrial DNA relative to nuclear DNA when glycerol was used as a carbon source than when glucose was used. Two criteria were used to determine the amount of mitochondrial DNA present: i) incorporation of radioactive precursors into the different DNA species; and ii) measurement of the mass of DNA from amounts of ultraviolet-absorbing material at the appropriate buoyant densities in isopycnic CsCl gradients. It is proposed that the two to three fold difference in the ratio of mitochondrial DNA to nuclear DNA in stationary phase cells grown in the presence of glycerol compared to glucose reflects an increased number of mitochondrial genomes in derepressed mitochondria. This difference, by a “genome dosage” effect, could account for the variations in the genetic parameter of the frequency of transmission, i.e., strains grown with glycerol as a carbon source contain more mitochondrial genomes than glucose-grown strains and thus will contribute more mitochondrial markers to the zygote.

Claire D. Goldthwaite

Papers

Effect of carbon source on the replication and transmission of yeast mitochondrial genomes.