| Summary: | 碩士 === 國立高雄師範大學 === 生物科技系 === 97 === Bacillus cereus, a food-bone pathogen, has been described to cause human illness such as vomiting and diarrhea. The alternative transcription factor σB is responsible for the transcription of genes that confer B. cereus general stress resistance, and favorable for bacterial survival in extreme conditions related to pathogenesis. The sigB gene cluster is composed of five genes, including of sigB, three regulators rsbV, rsbW, rsbY, and an open reading frame orf4. The functional role of RsbV, RsbW, and RsbY has been clearly demonstrated that is involved in σB regulation, but the function of orf4 remains to be explored. To characterize the function of orf4, recombinant protein rOrf4 was produced and an orf4-null mutant of B. cereus was generated with homologous recombination. Consequently, deletion of orf4 did not affect σB activation during 42℃ heat stress. Therefore we conclude that orf4 is not involved in σB activity. The comparision of amino acid sequence reveals Orf4 shares homology with bacterioferritin and DPS (DNA protection of starvation protein). Orf4 displayed ferroxidase activity, DNA bind ability to protect DNA against oxidative damage in vitro. Moreover orf4-null mutant exhibited a lower viability than wild-type under organic hydroperoxide treatment. Taken together, we propose that Orf4 may function as a dps-like bacterioferritin which sequester iron ion to eliminate free radical and shield DNA via direct binding.
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