Decrease in expression of the master operon of flagellin synthesis in a dnaA46 mutant of Escherichia coli

We examined the expression of the fliC, fliA and flhD genes in the dnaA46 mutant. In Northern blot analysis, the amounts of fliC, fliA, and flhD mRNA decreased in the dnaA46 mutant growing at 37°C but not at 28 °C. The promoter activity of each gene also decreased in this mutant at 37°C, but not at 28°C. The decrease in expression of the flhD gene was not related to the cAMP-catabolite activator protein (CAP) pathway. We tentatively conclude that DnaA protein is involved in the expression of the flhD gene by a mechanism independent of the cAMP-CAP pathway.