2000 Fiscal Year Final Research Report Summary
Molecular Mechanisms for Cellular Responses to Ionizing Radiation and Oxidative Stresses
| Project/Area Number |
10480132
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| Research Category |
Grant-in-Aid for Scientific Research (B).
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
環境影響評価(含放射線生物学)
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| Research Institution | KYOTO UNIVERSITY |
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Principal Investigator |
YONEI Shuji Kyoto University, Graduate School of Science, 大学院・理学研究科, 教授 (60093340)
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| Co-Investigator(Kenkyū-buntansha) |
ZHANG Qiu-mei Kyoto University, Graduate School Professor of Science Assistant Professor, 大学院・理学研究科, 助教授 (00260604)
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| Project Period (FY) |
1998 – 2000
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| Keywords | Ionizing Radiation / Reactive Oxygen Species / SH Oxidation / Thioredoxin / Redox Regulation / Glutathione / SoxR / OxyR |
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| Research Abstract |
Escherichia coli possesses a regulon which is induced in response to oxidative stress by superoxide-generating (redox-cycling) agents mediated by the soxRS regulator. Induction of the soxRS regulon occurs in two stages of transcriptional activation. SoxR protein that is directly activated by superoxide stress stimulates the transcription of the soxS gene, which in turn activates certain genes in the soxRS regulon. SoxR is a 34-kDa homodimer containing one redox-active [2Fe-2S] cluster in the polypeptide chain. Little is known about the molecular mechanisms of such activation process. The SoxR protein is also activated by diamide, a SH-oxidizing agent, under anaerobic conditions, indicating that the SoxR is activated via its redox state. We found that the induction of SoxS is enhanced in the mutants lacking the genes of the glutaredoxin and thioredoxin systems. On the other hand, the over-expression of reduced form of glutaredoxin decreased the level of SoxS induction by menadione. E.coli cells possess a specific defense system against H_2O_2 mediated by the transcriptional activator OxyR.The inactive form of OxyR protein present in unstressed cell is oxidized upon exposure to peroxide stress and converted into its active conformation as a transcriptional activator. Reversible intramolecular disulfide bond formation between Cys-199 and Cys-208 regulates the activity of OxyR.The present experiments were done to elucidate the role of thioredoxin, glutaredoxin and their reductase systems in oxidation and reduction of OxyR.By using the OxyR-specific antibody, we found that the oxidation-reduction of OxyR was affected by the redox states of thioredoxin and glutaredoxin in E.coli. The redox state of OxyR well correlated to the level and kinetics of the expression of kat G : : lacZ gene. The high level of β-galactosidase activity occurred in E.coli trxAgrxA mutant without treatment with H_2O^2. The mutant cells contained significant amount of activated form of OxyR.
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