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

Biogenesis of Mitochondria

Mitochondrial superoxide simutase. Site of synthesis and intramitochondrial localization.

The chromosomal DNA molecules of a standard laboratory strain of Saccharomyces cerevisiae have been separated into 12 well-resolved bands by orthogonal-field-alternation gel electrophoresis. DNA X DNA hybridization probes derived from cloned genes have been used to correlate this banding pattern with yeast's genetically defined chromosomes. The 12 bands are shown to represent 9 singlets and 3 comigrating doublets, thereby accounting for 15 chromosomes that were identified as I-XI and XIII-XVI. Because the three comigrating doublets could be readily resolved in certain laboratory yeast strains that contain chromosome-length polymorphisms relative to our standard strain, all 15 of these chromosomes could be displayed as a single band in at least one of four strains that were studied. A 16th chromosome (number XII), which is known to contain the genes for rRNA, does not reproducibly enter the gels. By making use of the band identifications, the previously unmapped fragment F8 was assigned to chromosome XIII. With the possible exception of chromosomes that differ greatly in size or electrophoretic behavior from all the known chromosomes, the results appear to define a complete "electrophoretic karyotype" for yeast.

https://www.pnas.org/content/pnas/82/11/3756.full.pdf

An electrophoretic karyotype for yeast

Saccharomyces cerevisiae cell cycle.

https://mmbr.asm.org/content/mmbr/54/3/211.full.pdf

PET genes of Saccharomyces cerevisiae.

The petite mutation in yeast. Loss of mitochondrial deoxyribonucleic acid during induction of petites with ethidium bromide.

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.

Dennis R. Cryer

Papers

The petite mutation in yeast. Loss of mitochondrial deoxyribonucleic acid during induction of petites with ethidium bromide.

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

The petite mutation in yeast. III. Nearest-neighbor analysis of mitochondrial DNA from normal and mutant cells