Schmidt Katherine A, Manna Adhar C, Cheung Ambrose L
Department of Microbiology, Dartmouth Medical School, Hanover, New Hampshire 03755, USA.
Infect Immun. 2003 Sep;71(9):5139-48. doi: 10.1128/IAI.71.9.5139-5148.2003.
Staphylococcus aureus is a gram-positive pathogen that is capable of expressing a variety of virulence proteins in response to environmental signals. Virulence protein expression in S. aureus is controlled by a network of regulatory loci including sarA and agr. The sarA/agr network is associated with the expression of cell wall-associated adhesins during exponential growth and the expression of secreted enzymes and toxins in the transition to post-exponential growth. A number of sarA homologs, including sarT and sarS, have been identified in the S. aureus genome. Previous studies have shown that sarA influences expression of both sarT and sarS in the global regulatory network. SarS has been shown to bind to the spa promoter to induce expression of protein A. SarT, one of the SarA homologs that represses hla expression and is repressible by SarA and agr, was found to induce sarS expression in this report. Northern blot analysis of sarS and spa expression in S. aureus RN6390, and the isogenic sarT, sarT sarA, and sarT agr mutants showed that while sarA regulated spa expression directly, the agr locus used sarT as an intermediary to regulate sarS, thus leading to spa repression in agr-activated cells. Gel shift and footprinting analysis showed that SarT binds to the sarS promoter, indicating that the interaction of the sarT gene product with the upstream region of sarS is likely direct. Induction of sarS and spa by SarT in agr(+) strains was confirmed by a tetracycline-inducible system to titrate sarT expression.
金黄色葡萄球菌是一种革兰氏阳性病原体，能够根据环境信号表达多种毒力蛋白。金黄色葡萄球菌中毒力蛋白的表达受包括sarA和agr在内的调控基因座网络控制。sarA/agr网络与指数生长期细胞壁相关黏附素的表达以及向指数后期生长转变过程中分泌酶和毒素的表达有关。在金黄色葡萄球菌基因组中已鉴定出许多sarA同源物，包括sarT和sarS。先前的研究表明，sarA在全局调控网络中影响sarT和sarS的表达。已证明SarS与spa启动子结合以诱导蛋白A的表达。SarT是抑制hla表达且可被SarA和agr抑制的SarA同源物之一，在本报告中发现其可诱导sarS表达。对金黄色葡萄球菌RN6390以及同基因的sarT、sarT sarA和sarT agr突变体中sarS和spa表达的Northern印迹分析表明，虽然sarA直接调节spa表达，但agr基因座利用sarT作为中介来调节sarS，从而导致agr激活细胞中spa的抑制。凝胶迁移和足迹分析表明，SarT与sarS启动子结合，表明sarT基因产物与sarS上游区域的相互作用可能是直接的。通过四环素诱导系统滴定sarT表达，证实了SarT在agr(+)菌株中对sarS和spa的诱导作用。
