Mitochondrial genome of yeast

The use of sulfite, one of the very first preservatives, has been greatly reduced because of reports of adverse effects on human health, especially in steroid-dependent asthmatics. It has been replaced in food preservation by the use of organic acids. In various studies, however, it has been found that preservatives are also acting as pro-oxidants and can even be mutagenic toward the mitochondrial genome of yeasts in aerobic environments. The potential for weak organic acid food preservatives to act as pro-oxidants in humans should receive much attention if only to reassure the public of the complete safety of these compounds (Piper, 1999). 

Although there is a 5-fold difference between the sizes of the mitochondrial genomes of yeast (84 kb) and mammals (16 kb), the number of proteins synthesized within mitochondria is similar. Proteins produced by mammalian mitochondria are those involved in electron-transport and oxidative-phosphorylation systems. These include cytochrome b, three subunits of cytochrome oxidase, one subunit of ATPase, and six subunits of NADH dehydrogenase. Apart from these differences, protein synthesis in mitochondria follows the same steps and mechanisms as those in the cytoplasm. 

Lessons from a small dispensable genome, the mitochondrial genome of yeast... 

The next step was the precise definition of the sequences involved in the excision process. The basic idea of the deletion model mentioned above was that the instability of the mitochondrial genome of yeast was due to the existence in each genome unit of a number of nucleotide sequences having enough homology to allow illegitimate, unequal recombination to take place. In this respect, clearly the GC clusters were at least as good candidates as the AT spacers. 

Before we move to these subjects in the following sections, it should be stressed that the organization of the mitochondrial genome of yeast points to the fact that in eukaryotic genetic systems, where so much of the DNA is non-coding, there is a real need for a molecular approach, because approaches based on classical genetics or on the study of gene products suffer from serious intrinsic limitations and are unable to provide an overall... 

Figure 2.21. Hypothetical superfolding of ori sequences from the mitochondrial genome of yeast, (a, a ) Superfolding of ori 3 and ori 5 base-pairing interactions take place between sequences /a and ra as well as between flanking sequences Zp. sequence is supposed to loop out. In ori 4 and ori 6, the size of the loop (132 bp) between sequences Zp and C would be considerably extended (by 70 bp) because of the insertion of clusters p and y. This does not occur, however, if these clusters take the configuration shown in (a), (b) Folding of ori I. In the case of ori 1, Zp cannot fold upon itself, but can interact with sequence r this interaction may also take place in ori 2, The overall result is no change in the size of the loop. Only in the case of ori 7, the loop would be larger by 30 bp, the size of cluster y. (From de Zamaroezy et al., 1984).

In conclusion, the evidence available at the present time appears to support the idea that the complex sequence organization of the mitochondrial genome of yeast corresponds to the needs of very active and finely regulated replication, transcription, and recombination processes. This seems to be achieved at the price of an exceptional genomic instability. 

These results are similar to the in vivo data on the effect of growth temperature on the structure and function of ori sequences in the mitochondrial genome of yeast (Goursot et al., 1988 see Part 2). In this case too, increasing temperature from 28°C to 33°C led to the melting of AT stems in the ori sequence of some petite mutants and to the consequent decrease of replicative ability. These results demonstrate direct (reversible) temperature effects on the secondary (and tertiary) structures of DNA and RNA. 

Baldacci G. and Bernardi G. (1982). Replication origins are associated with transcription initiation sequences in the mitochondrial genome of yeast. EMBO J. 1 987-994. 

Bernardi G. (1982b). The origins of replication of the mitochondrial genome of yeast. Trends in Biochem. Sci. 1 404-408. 

Bernardi G., Prunell A., Kopecka H. (1975). An analysis of the mitochondrial genome of yeast with restriction enzymes. In Molecular Biology of Nucleocytoplasmic Relationships (S. Puiseux-Dao, ed.) pp. 85-90, Elsevier, Amsterdam, The Netherlands. 

Bernardi G. (2005). Lessons from a small, dispensable genome the mitochondrial genome of yeast - review. Gene 354 189-200. 

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