DegU-P represses expression of the motility fla-che operon in Bacillus subtilis.
Bacillus subtilis implements several adaptive strategies to cope with nutrient limitation experienced at the end of exponential growth. The DegS-DegU two-component system is part of the network involved in the regulation of postexponential responses, such as competence development, the production of exoenzymes, and motility. The degU32(Hy) mutation extends the half-life of the phosphorylated form of DegU (DegU-P); this in turn increases the production of alkaline protease, levan-sucrase, and other exoenzymes and inhibits motility and the production of flagella. The expression of the flagellum-specific sigma factor SigD, of the flagellin gene hag, and of the fla-che operon is strongly reduced in a degU32(Hy) genetic background. To investigate the mechanism of action of DegU-P on motility, we isolated mutants of degU32(Hy) that completely suppressed the motility deficiency. The mutations were genetically mapped and characterized by PCR and sequencing. Most of the mutations were found to delete a transcriptional termination signal upstream of the main flagellar operon, fla-che, thus allowing transcriptional readthrough from the cod operon. Two additional mutations improved the sigmaA-dependent promoter sequence of the fla-che operon. Using an electrophoretic mobility shift assay, we have demonstrated that purified DegU binds specifically to the PA promoter region of the fla-che operon. The data suggest that DegU represses transcription of the fla-che operon, and they indicate a central role of the operon in regulating the synthesis and assembly of flagella.
Amati
Giuseppe
G
Dipartimento di Genetica e Microbiologia, Via Abbiategrasso 207, 27100 Pavia, Italy. waldemar.vollmer@uni-tuebingen.de.
Bisicchia
Paola
P
Galizzi
Alessandro
A
D000222:Adaptation, Physiological / Q000235:genetics*; D019677:Artificial Gene Fusion; D001412:Bacillus subtilis / Q000235:genetics / Q000502:physiology*; D001426:Bacterial Proteins / Q000378:metabolism*; D002633:Chemotaxis / Q000235:genetics; D004252:DNA Mutational Analysis; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology; D005407:Flagella / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D017930:Genes, Reporter; D009068:Movement; D009154:Mutation; D009876:Operon; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000235:genetics / Q000502:physiology; D012808:Sigma Factor / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics; D014158:Transcription, Genetic; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C066497:DegU protein, Bacteria; D012097:Repressor Proteins; D012808:Sigma Factor; D001616:beta-Galactosidase