0, 200 mM NaCl). The imidazole in the eluent was removed using a Centrifuge Biomax-5 column (Millipore, Billerica, MA, USA), and the AirR protein solution was supplemented with 30% glycerol and stored at −80°C until use. The full-length airS ORF was amplified using PCR with the e-airS-f and e-airS-r primers from S. aureus NCTC8325 genomic DNA, cloned into the expression vector pET28a (+), and transformed selleckchem into E. coli BL21 (DE3). Purification of 6-His-tagged AirS was performed following

the procedures of AirR purification except an overnight induction of 0.5 mM IPTG at 16°C. The purity of the proteins was determined by SDS-PAGE, and the protein concentration was determined using the BCA assay with bovine serum albumin as the standard. AirR phosphorylation in vitro For AirR phosphorylation

in vitro, we used lithium potassium acetyl phosphate as phosphoryl group donor. Briefly, 10 μM AirR was equilibrated in buffer containing 50 mM Tris at pH 7.4, 50 mM KCl, 5 mM MgCl2, and 10% glycerol (phosphorylation buffer). Lithium potassium acetyl phosphate (Sigma-Aldrich, St. Louis, MO, USA) was added to a final concentration of 50 mM, and this mixture was incubated for 60 min at 37°C [27]. We also used AirS for AirR phosphorylation in vitro. Briefly, 10 μl phosphorylation buffer containing 2 μM AirS and 10 mM ATP was used to initiate the autophosphorylation of AirS. After incubation at 25°C for 5 min, 10 μM AirR was added and the incubation was continued for another 10 min [22]. Electrophoretic mobility shift assay The DNA fragments containing

the promoter region were amplified from the S. aureus NCTC8325 Selleckchem Peptide 17 genomic DNA. The PCR products were labeled using a digoxigenin (DIG) gel shift kit (Roche, Indianapolis, IN, USA) according to the manufacturer’s instructions. The labeled fragment was incubated at 25°C for 15 min with various amounts of AirR in 10 μl of incubation buffer (10 mM Tris–HCl, pH 8.0, 100 mM NaCl, 1 mM EDTA). After incubation, the mixtures were electrophoresed in a 5% native polyacrylamide gel in 0.5 × Tris-borate-EDTA (TBE) buffer. The band shifts were detected and analyzed according to the manufacturer’s instructions. The images were obtained using ImageQuant Fossariinae LAS 4000 mini (GE, Piscataway, NJ, USA). The unlabeled fragments of each promoter were added to the labeled fragments at a ratio of approximately 50:1, respectively, as specific competitors (SCs). The unlabeled fragments of the pta ORF region (50-fold) were added as non-specific competitors (NCs). Statistics The data were analyzed using the T-test analysis of variance, with a P value of < 0.05 considered significant (one asterisk), P < 0.01 (two asterisks). Results Transcriptional profile of the airSR mutated strain To investigate the function of AirSR, we performed a cDNA microarray analysis using total RNA from the exponential growth stage. The microarray results indicated that approximately 190 genes were up-regulated (ratio > 2.0) and 290 genes were down-regulated (ratio < −2.0).