SarS, a SarA homolog repressible by agr, is an activator of protein a synthesis in Staphylococcus aureus
SarS, a SarA homolog repressible by agr, is an activator of protein a synthesis in Staphylococcus aureus
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DOI：
10.1128/iai.69.4.2448-2455.2001
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发表时间：
2001-04-01
影响因子：
3.1
通讯作者：
Manna, AC
中科院分区：
文献类型：
--
作者：
Cheung, AL;Schmidt, K;Manna, AC
蛋白A（spa）的表达被全局调节位点sarA和agr抑制。虽然SarA可以直接结合到spa启动子下调spa表达，agr抑制spa表达的机制尚不清楚。在部分释放的基因组中寻找SarA同源物时，我们发现了一个SarA同源物，编码一种250个氨基酸的蛋白质，命名为SarS，位于spa基因的上游。sarS在亲本菌株RN 6390中几乎检测不到表达，但在agr和sarA突变体中高度表达，这些突变体通常表达高水平的蛋白A。有趣的是，蛋白A的表达减少，在一个sarS突变体中检测到的免疫印迹，但返回到近亲本水平的补充sarS突变体。与xylE报告基因连接的158-和491-bp的SPA启动子片段的转录融合研究揭示，与亲本菌株相比，在sarS突变体中SPA启动子的转录也下调。有趣的是，在spa的表达增强agr突变体中agr sarS双突变体，但不是在sarA sarS双突变体中恢复到接近亲本水平。相关：与此不同的发现是，观察到agr突变体中增强的sarS表达被反式提供的sarA基因座抑制，但在从质粒表达RNAIII的sarA突变体中不受抑制。凝胶位移研究还揭示了SarS与158-bpspa启动子的特异性结合。两者合计，这些数据表明，agr基因座可能介导的温泉镇压抑制转录的sarS，激活温泉的表达。然而，sarA基因座下调spa表达的途径是sarS独立的。
The expression of protein A (spa) is repressed by global regulatory loci sarA and agr. Although SarA may directly bind to the spa promoter to downregulate spa expression, the mechanism by which agr represses spa expression is not clearly understood. In searching for SarA homologs in the partially released genome, we found a SarA homolog, encoding a 250-amino-acid protein designated SarS, upstream of the spa gene. The expression of sarS was almost undetectable in parental strain RN6390 but was highly expressed in agr and sarA mutants, strains normally expressing high level of protein A. Interestingly, protein A expression was decreased in a sarS mutant as detected in an immunoblot but returned to near-parental levels in a complemented sarS mutant. Transcriptional fusion studies with a 158- and a 491-bp spa promoter fragment linked to the xylE reporter gene disclosed that the transcription of the spa promoter was also downregulated in the sarS mutant compared with the parental strain. Interestingly, the enhancement in spa expression in an agr mutant returned to a near-parental level in the agr sarS double mutant but not in the sarA sarS double mutant. Correlating: with this divergent finding is the observation that enhanced sarS expression in an agr mutant was repressed by the sarA locus supplied in trans but not in a sarA mutant expressing RNAIII from a plasmid, Gel shift studies also revealed the specific binding of SarS to the 158-bp spa promoter. Taken together, these data indicated that the agr locus probably mediates spa repression by suppressing the transcription of sarS, an activator of spa expression. However, the pathway by which the sarA locus downregulates spa expression is sarS independent.