Schmidt K A, Manna A C, Gill S, Cheung A L
Department of Microbiology, Dartmouth Medical School, Hanover, New Hampshire 13755, USA.
Infect Immun. 2001 Aug;69(8):4749-58. doi: 10.1128/IAI.69.8.4749-4758.2001.
In searching the Staphylococcus aureus genome, we found several homologs to SarA. One of these genes, sarT, codes for a basic protein with 118 residues and a predicted molecular size of 16,096 Da. Northern blot analysis revealed that the expression of sarT was repressed by sarA and agr. An insertion sarT mutant generated in S. aureus RN6390 and 8325-4 backgrounds revealed minimal effect on the expression of sarR and sarA. The RNAIII level was notably increased in the sarT mutant, particularly in postexponential-phase cells, while the augmentative effect on RNAII was less. SarT repressed the expression of alpha-hemolysin, as determined by Northern blotting, Western blotting, and a rabbit erythrocyte hemolytic assay. This repression was relieved upon complementation. Similar to agr and sarA mutants, which predictably displayed a reduction in hla expression, the agr sarT mutant exhibited a lower level of hla transcription than the sarT mutant. In contrast, hla transcription was enhanced in the sarA sarT mutant compared with the single sarA mutant. Collectively, these results indicated that the sarA locus, contrary to the regulatory action of agr, induced alpha-hemolysin production by repressing sarT, a repressor of hla transcription.
在搜索金黄色葡萄球菌基因组时，我们发现了几个与SarA同源的基因。其中一个基因sarT编码一种含有118个氨基酸残基、预测分子大小为16,096 Da的碱性蛋白。Northern印迹分析表明，sarT的表达受sarA和agr的抑制。在金黄色葡萄球菌RN6390和8325 - 4背景中产生的插入型sarT突变体对sarR和sarA的表达影响最小。sarT突变体中RNAIII水平显著升高，尤其是在指数后期的细胞中，而对RNAII的增强作用较小。通过Northern印迹、Western印迹和兔红细胞溶血试验确定，SarT抑制α-溶血素的表达。这种抑制在互补后得以缓解。与可预测地显示hla表达降低的agr和sarA突变体类似，agr sarT突变体的hla转录水平低于sarT突变体。相反，与单个sarA突变体相比，sarA sarT突变体中的hla转录增强。总体而言，这些结果表明，与agr的调节作用相反，sarA基因座通过抑制hla转录的抑制因子sarT来诱导α-溶血素的产生。
