Study on the Determination Mechanism of Flagellar Number in Bacterial Cell.

在细菌细胞分裂周期中，各种生物合成过程在时空控制下进行，最终产生两个具有相同结构的子细胞。鞭毛可以被认为是研究细胞成分复制遗传控制的最合适的系统之一。鼠伤寒沙门菌细胞学研究表明，鞭毛数目的重复发生在特定的阶段，即细胞伸长期的末期。然而，我们发现，在鞭毛调控子特异性抗sigma因子基因缺陷的菌株中，鞭毛的重新合成发生在细胞伸长的整个时期。结果表明，反西格玛因子的负反馈控制在鞭毛数复制过程中起重要作用。随着细胞的伸长，细胞体积增大，细胞内抗sigma因子浓度降低，使鞭毛调控因子得以表达，引发鞭毛的新生合成。flhDC操纵子是鞭毛调控子的起始操纵子。对该操纵子的转录分析表明，其有效表达依赖于类核蛋白H-NS。H-NS已被证明可以调节细菌染色体的超卷曲结构。由于DNA复制过程中染色体拓扑结构的动态变化会影响H-NS与特定DNA区域的关联，因此鞭毛调控子的表达和鞭毛的合成可能通过DNA与H-NS的相互作用而受到DNA复制过程的调控。

During bacterial cell division cycle, various biosynthetic processes proceed under spatial and temporal controls and two daughter cells with the same structures are finally produced. Flagella can be considered as one of the most suitable systems to study genetic control of duplication of cellular constituents. Cytological study of Salmonella typhimurium indicated that the duplication of flagellar number occurs at the specific stage, the end of cell elongation period. However, it was found that, in the strains defective in the gene for anti-sigma factor specific for flagellar regulon, de novo synthesis of flagella occurs throughout cell elongation period. This result indicates that a negative feedback control exerted by the anti-sigma factor plays an important role in duplication process of flagellar number. As the cell elongates, the cell volume increases and the intracellular concentration of anti-sigma factor decreases, which allows the flagellar regulon expressed and results in initiation of de novo synthesis of flagella. The flhDC operon is known as an initiation operon of flagellar regulon. Transcriptional analysis of this operon revealed that its efficient expression is dependent on a nucleoid protein, H-NS. H-NS has been shown to modulate the supercoiling structure of bacterial chromosome. Because dynamic change of the topology of chromosome during DNA replication process can influence the association of H-NS with specific DNA regions, the expression of flagellar regulon and thus the synthesis of flagella may be regulated by DNA replication process through interaction of DNA with H-NS.