Genetic and molecular analyzes of bacterial flagellum which acts as a transcription-controlling apparatus

在鼠伤寒沙门氏菌鞭毛形态发生过程中，参与丝组装的基因只有在钩组装完成后才能充分表达。这种基因表达与形态发生的耦合是通过将鞭毛特异性抗sigma因子（FlgM）通过成熟的钩基体结构输出细胞而实现的。因此，鞭毛专用出口装置必须能够感知鞭毛结构的装配状态，并在钩装配的特定阶段开启鞭毛专用出口。本研究在分子水平上对这种出口开关机制进行了剖析。主要结论如下：(1)在钩子组装完成之前，FlgM的出口门被FlhB和RflH蛋白双重锁住。(2)这些锁在突变体中被打开，产生异常细长的缺乏钩的杆状体。这表明鱼钩长度监测系统测量的是鱼竿加上鱼钩的长度。(3) FlgM门还参与鞭毛后期蛋白FlgK、FlgL、fld和flc的输出控制。FlhB还负责关闭钩子组装完成后的钩子蛋白输出过程。(4)分离出RflH锁本构打开的突变体。这些突变体的遗传分析表明，至少有两种蛋白质参与RflH锁的打开过程。(5) FlhB锁在吊钩装配初期打开，RflH锁在吊钩装配完成后打开。

During flagellar morphogenesis in Salmonella typhirnurium, the genes involved in filament assembly are expressed fully only after completion of hook assembly. This coupling of gene expression to morphogenesis is achieved by exporting the flagellum-specific anti-sigma factor, FlgM, out of the cell through the mature hook-basal body structure. Therefore, the flagellum-specific export apparatus must be able to sense the assembly state of the flagellar structure and to turn on FlgM export at the specific stage of hook assembly. In this study, this export switching machinery was dissected at a molecular level. The main conclusions are as follows. (1) The export gate for FlgM is double locked by FlhB and RflH proteins before completion of hook assembly. (2) These locks are opened in the mutants which produce abnormally elongated rods lacking hooks. This indicates that the monitor system of hook length measures the length of the rod plus the hook. (3) The FlgM gate is also involved in the export control of the late flagellar proteins, FlgK, FlgL, FliD, and FliC.FlhB is also responsible for shutting-off process of the export of hook protein after completion of hook assembly. (4) Mutants in which the RflH lock is opened constitutively were isolated. Genetic analysis of these mutants suggested that at least two proteins are involved in the opening process of the RflH lock. (5) The FlhB lock is opened at the early stage of hook assembly, whereas the RflH lock is opened upon completion of hook assembly.