A novel anti-anti-activator mechanism regulates expression of the Pseudomonas aeruginosa type III secretion system
A novel anti-anti-activator mechanism regulates expression of the Pseudomonas aeruginosa type III secretion system
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DOI：
10.1111/j.1365-2958.2004.04128.x
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发表时间：
2004-07-01
影响因子：
3.6
通讯作者：
Yahr, TL
中科院分区：
文献类型：
--
作者：
Dasgupta, N;Lykken, GL;Yahr, TL
铜绿假单胞菌III型分泌系统（TTSS）的表达与细胞的分泌状态相关联。环境信号如钙耗竭激活III型分泌通道，因此III型基因转录被去抑制。ExsA和ExsD这两种蛋白质先前被证明在将转录与分泌偶联中起作用。ExsA是TTSS基因转录的激活剂，ExsD是ExsA的抗激活剂。在缺乏环境分泌线索的情况下，ExsD结合ExsA并抑制转录。在这里，我们描述了表征ExsC作为TTSS表达的抗-抗-激活剂。TTSS的转录在exsC突变体中被抑制，并且在ExsC过表达时被去抑制。在不存在exsD的情况下，对exsC的转录依赖性减轻，表明ExsC和ExsD一起起作用以调节转录。与这一想法一致，ExsC与ExsD在细菌双杂交和共纯化测定中相互作用。我们提出了一个模型，其中抗-抗-激活剂（ExsC）在低Ca 2+条件下结合并螯合抗激活剂（ExsD），释放ExsA并允许TTSS的转录。铜绿假单胞菌系统代表了控制TTSS转录的抗激活剂/抗-抗-激活剂对的第一个实例。
Expression of the Pseudomonas aeruginosa type III secretion system (TTSS) is coupled to the secretion status of the cells. Environmental signals such as calcium depletion activate the type III secretion channel and, as a consequence, type III gene transcription is derepressed. Two proteins, ExsA and ExsD, were shown previously to play a role in coupling transcription to secretion. ExsA is an activator of TTSS gene transcription, and ExsD is an anti-activator of ExsA. In the absence of environmental secretion cues, ExsD binds ExsA and inhibits transcription. Here, we describe the characterization of ExsC as an anti-anti-activator of TTSS expression. Transcription of the TTSS is repressed in an exsC mutant and is derepressed upon ExsC overexpression. The dependence on exsC for transcription is relieved in the absence of exsD, suggesting that ExsC and ExsD function together to regulate transcription. Consistent with this idea, ExsC interacts with ExsD in bacterial two-hybrid and co-purification assays. We propose a model in which the anti-anti-activator (ExsC) binds to and sequesters the anti-activator (ExsD) under low Ca2+ conditions, freeing ExsA and allowing for transcription of the TTSS. The P. aeruginosa system represents the first example of an anti-activator/anti-anti-activator pair controlling transcription of a TTSS.