Publikationsserver der RWTH Aachen University
Die Kontrolle der Transkription in den Mitochondrien des Modellorganismus Schizosaccharomyces pombe
Abstract
dc:descriptionGenes encoded by the mitochondrial genome were characterised in various organisms, but many aspects of transcription, processing and degradation are poorly understood. The steady state level of mitochondrial transcription can not be controlled by regulation of the rudimentary promoters, in contrast to the nuclear encoded genes. The disturbance of mitochondrial transcription can lead to the development of mitochondriopathies. The molecular mechanisms of this class of diseases have become a target of ambitious research projects. Regarding the mitochondrial genome organisation, there are higher similarities between human and Schizosaccharomyces pombe than between human and Saccharomyces cerevisiae, making fission yeast the more suitable model organism. To get a first impression of the transcription-control in mitochondria, the Wild type grown on different carbon sources at various temperatures was investigated. By a newly established transcriptome profiling, using quantitative Real time PCR, it could be shown, that derepressing conditions as well as heat stress led to an increase of mitochondrial steady state levels. In both cases the increase of the mitochondrial steady state levels (> factor 6) was stronger than the accumulation of nuclear transcripts of genes influencing the mitochondrial transcriptome (< factor 2). The combination of this conditions led to an increased demand of mitochondrial transcription resulting in increased steady state levels of nuclear encoded transcripts (> factor 4). Mutants which partly lost the ability to grow on non-fermentable carbon source were analysed to identify genes involved in the control of the mitochondrial transcriptom. Using DNA-libraries to complement the growth defects, the open reading frame (ORF) SPCC1183.03c, called Sp-pet127, was identified. The disruption of this gene decreased the ability to grow on non-fermentable carbon sources at elevated temperatures. Bioinformatic investigations showed that homologues of this gene are present in over 60 organisms. Qualitative analysis of the mitochondrial transcriptome of the disruptant indicated no processing defects in S. pombe. The disruption of this gene resulted in a strong increase of most of the mitochondrial transcripts while the overexpression of this ORF led to a decrease of the steady state levels. Because homologs of Sp-pet127 were found in organisms lacking polyadenylation of mitochondrial transcripts, these genes present another possibility to regulate transcript stability. The 5´-end of the transcripts is decisive for the control and defects at this end led to an enhanced degradation. The heterologe expression of Sp-pet127 in S. cerevisae complemented the effects of the disruption of S. cerevisiae homolog PET127. By overexpressing this Sp-pet127 in different disruptants, it could be shown that a mitochondrially localised complex consisting of a Helikase (rpm2) and an RNase (rpm1) is responsible for the generation of the ends of the mature transcripts, but not involved in general RNA turnover. Another gene, which was analysed in detail, was the ORF SPAP8A3.14c (Sp-sls1). The disruption lead to a total loss of respiration and the investigation of the mitochondrial transcriptome showed that especially the steady state levels of intron-containing genes like cox1 and cob are strongly decreased. By the use of a mitochondrially intronless strain, it could be shown that the observed reduction was not induced by intron-processing defects, but a lack of transcript stabilisation. This theory is supported by the observation that Sp-sls1 is able to stabilise incorrect processed transcripts of cob increasing the steady state level, regardless which end(s) showed processing defects. New important aspects of the knowledge about mitochondrial transcription control could be gained by analysing involved genes in this work. Sp-pet127 was identified as a factor involved in control of transcript quality and Sp-sls1, is a gene which stabilises certain transcripts and is crucial in coordination of transcription and translation.
Degree
thesis:*- Grantor dc:publisher
- Publikationsserver der RWTH Aachen University
- Year dc:date
- 2010
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Speer, Falk
- Contributors dc:contributor
-
- Schäfer, Bernd
Subjects
dc:subject × 15Rights
dc:rights- Statement dc:rights
-
- info:eu-repo/semantics/openAccess
- Language dc:language
- ger