Negative regulation by fliD, fliS, and fliT of the export of the flagellum-specific anti-sigma factor, FlgM, in Salmonella typhimurium

The fliD operon of Salmonella typhimurium consists of three flagellar genes, fliD, fliS, and fliT, and is transcribed in this order. It has been shown that an fliD::Tn10 mutation causes an excess export of the flagellum-specific anti-sigma factor, FlgM, resulting in an overexpression of flagellar class 3 operons. In this study, using gene-disruption mutants in the individual genes in the fliD operon, we showed that mutations in any one of the genes in the operon enhanced both FlgM export and the expression of flagellar regulon. This indicates that all three genes in the operon are involved in the negative regulation of FlgM export.