Cellular levels and activity of the flagellar sigma factor FliA of Escherichia coli are controlled by FIgM-modulated proteolysis
Cellular levels and activity of the flagellar sigma factor FliA of Escherichia coli are controlled by FIgM-modulated proteolysis
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DOI：
10.1111/j.1365-2958.2007.05770.x
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发表时间：
2007-07-01
影响因子：
3.6
通讯作者：
Hengge, Regine
中科院分区：
文献类型：
--
作者：
Barembruch, Claudia;Hengge, Regine
在大肠杆菌中，鞭毛调节子由60多个基因组成，分为三个层次和时间调节的转录类别。鞭毛σ因子FIiA（all）负责3类表达，并且在鞭毛组装的早期阶段，被其抗σ因子FlgM抑制。鞭毛钩基体形成能够分泌鞭毛亚基和FlgM的III型分泌系统。这导致释放并因此激活FliA和3类表达。在这里，我们表明，FliA也受到蛋白水解，主要取决于Lon蛋白酶。FlgM不仅充当抗西格玛因子，而且还保护FliA不被降解。基于对实验诱导的鞭毛级联以及在运动菌株的生长周期中随时间的定量测量，我们表明FliA蛋白水解平行于3类表达增加，即与FlgM分泌和FliA最高活性的阶段相关。因此，当FIgM由于分泌或突变而不可用时，并且RNA聚合酶相互作用在转录起始循环期间仅是瞬时的，蛋白酶可以降解FIiA。离子突变体的实验表明，Lon蛋白酶和FliA降解保持适当的FliA：FIGM化学计量诱导后的鞭毛系统，从而有助于及时关闭该系统。
In Escherichia coli the flagellar regulon consists of more than 60 genes organized in three hierarchically and temporally regulated transcriptional classes. The flagellar sigma factor FIiA (all) is responsible for class 3 expression and, in the early phase of flagellar assembly, is inhibited by its anti-sigma factor FlgM. The flagellar hook basal body forms a type III secretion system capable of secreting both flagellar subunits and FlgM. This results in release and therefore activation of FliA and class 3 expression. Here we demonstrate that FliA is also subject to proteolysis which mainly depends on Lon protease. FlgM not only acts as an anti-sigma factor but also protects FliA from being degraded. Based on quantitative measurements over time upon experimental induction of the flagellar cascade as well as during the growth cycle of a motile strain, we show that FliA proteolysis increases in parallel to class 3 expression, i.e. correlates with FlgM secretion and the phase of highest activity of FliA. Thus, when FIgM is not available due to secretion or mutation, and with RNA polymerase interaction being only transient during the transcription initiation cycle, the proteases can degrade FIiA. Experiments with a Ion mutant indicate that Lon protease and FliA degradation maintain appropriate FliA : FIgM stoichiometry upon induction of the flagellar system and thereby contribute to timely shut-off of this system.