Mitochondria are organelles which derived from bacteria during endosymbiosis. It is assumed that an archaebacterium absorbed an α-proteobacterium which developed to an essential and autonomous organelle of the host. Most of the genes were transferred to the nucleus, but nevertheless the mitochondria contain a functional genome, which is organized in so called nucleoids. In the budding yeast Saccharomyces cerevisiae, the mitochondrial DNA (mtDNA) encodes eight proteins, two rRNAs and several tRNAs, which are necessary for respiratory chain activity. The mitochondrial genome must be replicated, positioned and inherited to the daughter cells. Some proteins, which play a pivotal role in these processes like the DNA polymerase Mip1 or the DNA packaging protein Abf2, are known and well characterized. However, many proteins, which participate in these mechanisms, are still unknown. Hence the main goal of this study was to identify additional genes and proteins, which are required for the inheritance and maintenance of the mitochondrial genome in Saccharomyces cerevisiae. For this purpose, several high-throughput, genome-wide screens were performed using the MATa yeast deletion library, which contains about 4,800 strains with deletions of non-essential genes. The library was screened for deletion strains which lose their mtDNA after a certain time or independently of respiration. In addition, strains losing the mitochondrial DNA after being exposed to oxidative stress and strains retaining their wildtype mtDNA in presence of hypersuppressive mtDNA were searched for. The hypersuppressive mtDNA suppresses the wildtype mtDNA in most cases and gets inherited. Several candidates were identified in the different screens. For a further characterization of 16 of the identified deletion strains the nucleoids and mitochondrial as well as the vacuolar morphology were analyzed. Moreover, a possible function of the deletion genes and their proteins was suggested and analyzed wherever applicable. For instance, it was shown in this work that Ybr062c is not involved in the repair of mtDNA. Moreover, the protein Rrg1 is potentially a tRNA synthetase. The deletion strain of the TIM23 complex protein Mgr2 showed a wildtype ultrastructure in the electron microscope and Mgr2 was distributed evenly all over the mitochondrial network.
|School:||Universitaet Bayreuth (Germany)|
|Source:||DAI-C 81/4(E), Dissertation Abstracts International|
|Subjects:||Genetics, Molecular biology, Bioinformatics|
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