Expression of multiple flagellin-encoding genes of Proteus mirabilis.
The overproduction of flagella is a distinguishing characteristic of Proteus mirabilis swarmer cell differentiation. The synthesis of flagellin, the principal protein composing the flagellar filament, is coordinately regulated as part of a larger regulon of genes whose expression is a prerequisite in urinary pathogenesis. In this report, the regulation of expression of the flaA locus, comprising flaA and flaB, two tandemly linked and nearly identical copies of flagellin-encoding genes, is examined. Transcriptional expression studies reveal that flaA, but not flaB, is expressed by wild-type cells, and flaA transcription increases eightfold during differentiation. The flaA transcriptional start site for both swimmer and swarmer cells was determined to be located at a guanine, 8 bases downstream of the flaA sigma 28 promoter. FlaA- mutants are nonmotile and undifferentiated and do not synthesize flagellin, while FlaB- mutants are wild type, thus verifying that FlaA is the sole flagellin produced by wild-type cells and that flaB is silent. FlaA- mutants frequently revert to a Mot+ phenotype that is antigenically distinct from that of wild-type cells. Southern blot analysis of the flaA Mot+ revertants reveals a deletion of between 2 and 7kb in the flaA locus. Biochemical analyses of revertant flagellin indicate major changes in protein size and composition but conservation of the first 28 N-terminal residues. The result of this process is to produce an antigenically distinct flagellum that may be significant in ensuring the survival of P. mirabilis during pathogenesis.
Center of Marine Biotechnology, University of Maryland Biotechnology Institute, Baltimore 21202.
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D000942:Antigens, Bacterial / Q000235:genetics / Q000276:immunology; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D002454:Cell Differentiation; D002465:Cell Movement; D005407:Flagella / Q000235:genetics* / Q000276:immunology; D005408:Flagellin / Q000235:genetics* / Q000276:immunology; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial / Q000235:genetics*; D014644:Genetic Variation; D008957:Models, Genetic; D008969:Molecular Sequence Data; D011513:Proteus mirabilis / Q000235:genetics* / Q000276:immunology; D014158:Transcription, Genetic
D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D005408:Flagellin; C076733:FlaD protein, Bacteria