Multiple factors regulate the expression of in .

Introduction: The gene cluster, encoding the sole iron-sulfur (Fe-S) cluster assembly system in , was recently shown to be up-regulated in response to oxidative stressors and Fe limitation.

Methods: In this study, luciferase reporter fusion assays, electrophoretic gel mobility shift assays (EMSA) and transcription assays (IVT) were used to dissect the and acting factors that regulate the expression of .

Results And Discussion: Results showed deletion of , for the only Fur-family transcriptional regulator in , resulted in >5-fold increases in luciferase activity under the control of the promoter (P<0.01), as compared to the parent strain, UA159 when the reporter strains were grown in medium with no supplemental iron. Site-directed mutagenesis of a PerR-box in the promoter region led to elevation of the reporter activity by >1.6-fold (<0.01). In an EMSA, recombinant PerR (rPerR) was shown to bind to the cognate promoter leading to mobility retardation. On the other hand, the reporter activity was increased by >84-fold (P<0.001) in response to the addition of cysteine at 4 mM to the culture medium. Deletion of , for a LysR-type of transcriptional regulator, led to reduction of the reporter activity by >11.6-fold (<0.001). Addition of recombinant CysR (rCysR) to an EMSA caused mobility shift of the promoter probe, indicative of rCysR-promoter interaction, and rCysR was shown to enhance transcription under the direction of promoter . These results suggest that multiple factors are involved in the regulation of expression in response to environmental cues, including cysteine and Fe availability, consistent with the important role of in physiology.