SEQUENCE AND GENETIC-ANALYSIS OF MULTIPLE FLAGELLIN-ENCODING GENES FROM PROTEUS-MIRABILIS

Surface-induced overproduction of flagellin is one of the hallmarks of Proteus mirabilis swarmer cell differentiation. In this study, we ana lyzed the nucleotide (nt) and amino acid (aa) sequences, and expressio n of the P. Mirabilis flagellin-encoding gene (fliC) region. The nt se quence analysis of a 3567-bp region reveals three ORFs, each with homo logy to known Escherichia coli flagellar genes. The first ORF correspo nds to fliD, the gene encoding the flagellar filament capping protein, FliD (HAP2). The second and third ORFs are highly homologous to each other and to fliC genes from many other Gram- bacteria. To distinguish between the two alleles, we have designated these genes fliC1 and fli C2. Sequences highly homologous to promoter sites for the alternate si gma factor of RNA polymerase, sigma(28), are found 5' to the start of each gene. Additionally, both fliC1 and fliC2 have a conserved direct tandem repeat (DTR) sequence upstream from the sigma(28) promoter that may have functional significance in the transcriptional control of fl iC expression during swarmer cell differentiation. Both FliC1 and FliC 2 were produced in E. coli, but only FliC1 could complement FliC(-) mu tants of E. coli. Southern hybridization data indicate the presence of fliC1 and fliC2 in six distinct P. mirabilis strains, indicating that multiple flagellin-encoding genes are common in P. mirabilis. Hybridi zation data also suggest the presence of a third flagellin-encoding ge ne, fliC3, in all isolates. The possible significance of multiple fliC in swarmer cell differentiation is discussed.