Multiple factors regulate the expression of sufCDSUB in Streptococcus mutans

Results showed deletion of <i>perR</i>, for the only Fur-family transcriptional regulator in <i>S. mutans</i>, resulted in >5-fold increases in luciferase activity under the control of the <i>sufCDSUB</i> 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 (<i>P</i><0.01). In an EMSA, recombinant PerR (rPerR) was shown to bind to the cognate <i>sufCDSUB</i> 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 <i>cysR</i>, for a LysR-type of transcriptional regulator, led to reduction of the reporter activity by >11.6-fold (<i>P</i><0.001). Addition of recombinant CysR (rCysR) to an EMSA caused mobility shift of the <i>sufCDSUB</i> promoter probe, indicative of rCysR-promoter interaction, and rCysR was shown to enhance <i>sufC</i> transcription under the direction of <i>sufCDSUB</i> promoter <i>in vitro</i>. These results suggest that multiple factors are involved in the regulation of <i>sufCDSUB</i> expression in response to environmental cues, including cysteine and Fe availability, consistent with the important role of <i>sufCDSUB</i> in <i>S. mutans</i> physiology.