Department of Chemistry, York University, Toronto, Ontario, Canada.
PLoS One. 2012;7(8):e43998. doi: 10.1371/journal.pone.0043998. Epub 2012 Aug 30.
fmtA encodes a low-affinity penicillin binding protein in Staphylococcus aureus. It is part of the core cell wall stimulon and is involved in methicillin resistance in S. aureus. Here, we report that the transcription factor, SarA, a pleiotropic regulator of virulence genes in S. aureus, regulates the expression of fmtA. In vitro binding studies with purified SarA revealed that it binds to specific sites within the 541-bp promoter region of fmtA. Mutation of a key residue of the regulatory activity of SarA (Arg90) abolished binding of SarA to the fmtA promoter, suggesting that SarA binds specifically to the fmtA promoter region. In vivo analysis of the fmtA promoter using a lux operon reporter fusion show high level expression following oxacillin induction, which was abrogated in a sarA mutant strain. These data suggest that SarA is essential for the induction of fmtA expression by cell wall-specific antibiotics. Further, in vitro transcription studies show that SarA enhances fmtA transcription and suggest that regulation of fmtA could be via a SigA-dependent mechanism. Overall, our results show that SarA plays a direct role in the regulation of fmtA expression via binding to the fmtA promoter.
fmtA 在金黄色葡萄球菌中编码一种低亲和力青霉素结合蛋白。它是核心细胞壁刺激物的一部分，参与金黄色葡萄球菌中甲氧西林耐药性的形成。在这里，我们报告转录因子 SarA 是金黄色葡萄球菌中毒力基因的多效调节剂，调节 fmtA 的表达。与纯化的 SarA 的体外结合研究表明，它与 fmtA 启动子的 541bp 启动子区域内的特定位点结合。SarA 调节活性的关键残基（Arg90）的突变消除了 SarA 与 fmtA 启动子的结合，表明 SarA 特异性地与 fmtA 启动子区域结合。使用 lux 操纵子报告融合物对 fmtA 启动子进行体内分析表明，在 oxacillin 诱导后高水平表达，而在 sarA 突变株中则被阻断。这些数据表明 SarA 对于细胞壁特异性抗生素诱导 fmtA 表达是必需的。此外，体外转录研究表明 SarA 增强了 fmtA 的转录，并表明 fmtA 的调节可能通过 SigA 依赖性机制进行。总的来说，我们的结果表明，SarA 通过与 fmtA 启动子结合，在 fmtA 表达的调节中发挥直接作用。
