Expression of the multidrug resistance transporter NorA from Staphylococcus aureus is modified by a two-component regulatory system

To dissect genetically the regulation of NorA, a multidrug transporter of S taphylococcus aureus, we analyzed the differential expression of the norA p romoter using a transcriptional fusion with a P-lactamase reporter gene. Ex pression studies with an arlS mutant revealed that the norA promoter is Arl S dependent. The arlR-arlS locus was shown to code for a two-component regu latory system. The protein ArlR has strong similarity to response regulator s, and ArlS has strong similarity to protein histidine kinases. We have als o analyzed the 350-bp region upstream of the Shine-Dalgarno sequence of nor A by gel mobility shift experiments. It was shown that only the 115-bp regi on upstream of the promoter was necessary for multiple binding of an 18-kDa protein. From transcriptional fusions, we have localized four different pu tative boxes of 6 bp, which appear to play a role in the binding of the 18- kDa protein and in the up-regulation of norA expression in the presence of the arlS mutation. Furthermore, the gel mobility shift of the 18-kDa protei n was modified in the presence of the arlS mutation, and the arlS mutation altered the growth-phase regulation of NorA. These results indicate that ex pression of norA is modified by a two-component regulatory system.