Student Research - Biology
Aaron Daugherty
Induction of the Shigella flexneri isc operon in intracellular and extracellular conditions
Abstract: Shigella flexneri contains the iscRSUA locus which is predicted to encode proteins that mediate construction and/or repair of iron-sulfur clusters. A cDNA fragment generated from S.flexneri RNA using a primer located in the iscA gene could be amplified by PCR using primers in iscR indicating that the Shigella iscRSUA genes are transcribed as a single strand of messenger RNA. GFP reporter and real time RT-PCR studies were done to investigate environmental signals that regulate expression of the S. flexneri isc operon. The isc operon was transcribed at a lower level when S. flexneri was grown in iron-rich media as compared to iron-limited media. Transcription of the isc operon increased when Shigella was exposed to the superoxide generator phenazine methosulfate or to hydrogen peroxide. This induction occurred in S. flexneri strains without the oxidative stress responsive transcriptional activators OxyR and SoxRS, suggesting that these two proteins are not required for isc expression in response to oxidative stress. Expression of the isc operon increased after invasion of colon-derived Henle cells and this increased expression was also independent of OxyR and SoxRS.
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