Hahnenberger K M, Shapiro L
J Mol Biol. 1987 Mar 5;194(1):91-103. doi: 10.1016/0022-2836(87)90718-2.
The bacterial flagellum is a complex structure composed of a transmembrane basal body, a hook, and a filament. In Caulobacter crescentus the biosynthesis and assembly of this structure is under temporal and spatial control. To help to define the order of assembly of the flagellar components and to identify the genes involved in the early steps of basal body construction, mutants defective in basal body formation have been analyzed. Mutants in the flaD flaB flaC gene cluster were found to be unable to assemble a complete basal body. The flaD BC motC region was cloned and the genes were localized by subcloning and complementation analysis. A series of Tn5 insertion mutations in the flaD BC region were mapped. Complementation analysis of the Tn5 insertion mutants indicated the existence of at least four transcriptional units in the region and identified the presence of two new genes designated flbN and flbO. Mutants in flbN, flaB, flaC and flbO were unable to assemble any basal body structure and are likely to be involved in the early steps of basal body formation. The flaD mutant, however, was found to contain a partially assembled basal body consisting of the rod and three hook-distal rings. All of the mutants in this cluster exhibited pleiotropic effects on the expression of other flagellar and chemotaxis functions, including the level of synthesis of flagellins, the hook protein and hook protein precursor, and the level of chemotaxis methylation.
细菌鞭毛是一种由跨膜基体、钩形鞘和鞭毛丝组成的复杂结构。在新月柄杆菌中，这种结构的生物合成和组装受到时间和空间的控制。为了确定鞭毛组件的组装顺序，并识别参与基体构建早期步骤的基因，对基体形成有缺陷的突变体进行了分析。发现flaD、flaB、flaC基因簇中的突变体无法组装完整的基体。克隆了flaD BC motC区域，并通过亚克隆和互补分析对基因进行了定位。绘制了flaD BC区域一系列Tn5插入突变的图谱。对Tn5插入突变体的互补分析表明该区域至少存在四个转录单元，并鉴定出两个新基因flbN和flbO。flbN、flaB、flaC和flbO中的突变体无法组装任何基体结构，可能参与基体形成的早期步骤。然而，发现flaD突变体含有一个部分组装的基体，由杆状物和三个钩形鞘远端环组成。该基因簇中的所有突变体对其他鞭毛和趋化功能的表达均表现出多效性影响，包括鞭毛蛋白、钩形鞘蛋白和钩形鞘蛋白前体的合成水平，以及趋化甲基化水平。
