| Summary: | 碩士 === 國立臺灣大學 === 植物科學研究所 === 97 === Cells growing aerobically are exposed to reactive oxygen species (ROS) generated during metabolism. These ROS can seriously damage the cell by reacting with cellular components, causing oxidative stress and cell death. The aim of this study is to investigate roles of two S. cerevisiae genes, YGR021w and YGL026c (tryptophan synthase, TRP5), in oxidative stress response by taking genetic, molecular and microarray approaches. Firstly, YGR021w is predicted to encode a protein belonging to a conserved novel protein family, namely DUF28. The results showed: (1) YGR021w expression was repressed by oxidative stress factors; (2) Deletion of YGR021w led to enhanced tolerance to hydrogen peroxide and heat shock stress, and YGR021w over-expression had opposite effects; (3) Stress-induced expression of oxidative response-related genes in YGR021w-deleted strain was faster and stronger compared to the wild-type strain (WT) ; (4) Microarray-based transcriptome analysis revealed enhanced induction of genes involved in oxidative response, carbohydrate metabolism in YGR021w-deleted strain compared to the WT. As the first report, these results together indicated that YGR021w plays a negative role in yeast response to oxidative stress. Secondly, role of TRP5 in oxidative stress has not been elucidated until this study. The results showed: (1) TRP5 expression was induced by oxidative stress factors; (2) Deletion of the TRP5 led to remarkably increased sensitivity to various oxidative stresses and hydrophobic toxic compounds, while complementation rescued some of these defects; (3) Stress-induced expression of oxidative response-related genes in TRP5-deleted strain was much reduced compared to the WT; (4) Exogenous supplement of plant hormone IAA, enhanced tolerance to oxidative stress in the WT and the TRP5-deleted strain; (5) Microarray analysis revealed decreased expression of genes involved in stress tolerance and protein degradation in the deleted strain compared to the WT. Therefore, in addition to possible loss of cell structure integrity, the accumulation of abnormal proteins under stress condition in TRP5-deleted strain, which is not capable of degrading and removing such proteins, may account for the increased sensitivity of TRP5-deleted strain to oxidative stress. These results pointed out that TRP5 plays an important role in yeast stress response. Taken together, the results suggest that both negative and positive elements are required to involve and coordinate to achieve proper and efficient response in yeast to oxidative stress.
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