NEGATIVE FEEDBACK FROM A PROTEUS CLASS-II FLAGELLUM EXPORT DEFECT TO THE FLHDC MASTER OPERON CONTROLLING CELL-DIVISION AND FLAGELLUM ASSEMBLY

The Proteus mirabilis flagellum class I flhDC operon was isolated, and its transcript was shown to originate from a sigma(70) promoter 244 b p 5' of fIhD and 29 bp 3' of a putative cyclic AMP receptor protein-bi nding site. Expression of this regulatory master operon increased stro ngly as cells differentiated into elongated hyper-flagellated swarm fi laments, and cell populations artificially overexpressing flhDC migrat ed sooner and faster. A class II flhA transposon mutant was reduced in flagellum class III gene expression, as would be expected from the Fl gM anti-sigma(28) accumulation demonstrated in Salmonella typhimurium, but was unexpectedly also reduced in cell elongation, Were, we show t hat levels of flhDC transcript were ca 10-fold lower in this flagellum export mutant, indicating that in cells defective in flagellum assemb ly, there is additional negative feedback via flhDC. In support of thi s view, artificial overexpression of flhDC in the flhA mutant restored elongation but not class III flagellum gene transcription.