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.
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Center of Marine Biotechnology, University of Maryland Biotechnology Institute, Baltimore 21202.
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