Transcriptional Profiling Analysis of the Global Regulator NorG, a GntR-Like Protein of Staphylococcus aureus

The GntR-like protein NorG has been shown to affectStaphylococcus aureus genes involved in resistance to quinolones and β-lactams, such as those encoding the NorB and AbcA transporters. To identify the target genes regulated by NorG, we carried out transcriptional-profiling assays usingS. aureus RN6390 and its isogenicnorG ::cat mutant. Our data showed that NorG positively affected the transcription of global regulatorsmgrA ,arlS , andsarZ . The three putative drug efflux pump genes most positively affected by NorG were the NorB efflux pump (5.1-fold), the MmpL-like protein SACOL2566 (5.2-fold), and the BcrA-like drug transporter SACOL2525 (5.7-fold) genes. TheS. aureus predicted MmpL protein showed 53% homology with the MmpL lipid transporter ofMycobacterium tuberculosis , and the putative SACOL2525 protein showed 87% homology with the bacitracin drug transporter BcrA ofStaphylococcus hominis . Two pump genes most negatively affected by NorG were the NorC (4-fold) and AbcA (6-fold) genes. Other categories of genes, such as those participating in amino acid, inorganic ion, or nucleotide transporters and metabolism, were also affected by NorG. Real-time reverse transcription (RT)-PCR assays formgrA ,arlS ,sarZ ,norB ,norC ,abcA ,mmpL , andbcrA -like were carried out to verify microarray data and showed the same level of up- or downregulation by NorG. ThenorG mutant showed a 2-fold increase in resistance to norfloxacin and rhodamine, both substrates of the NorC transporter, which is consistent with the resistance phenotype conferred by overexpression ofnorC on a plasmid. These data indicate that NorG has broad regulatory function inS. aureus .