Characterization of six flagellin genes in the H3, H53 and H54 standard strains of Escherichia coli

Six flagellin genes in three H standard Escherichia colt strains for H3, H53 and H54 were characterized. Each strain has two flagellin genes, one of which is expressed as its standard H antigen. A pair of flagellin genes flkA3 (encoding for H3 antigen) and fliC16 (H16) was cloned from Bi7327-41, flkA53 (H53) and fliC-53 from E480-68, and flmA54 (H54) and fliC-54 from E223-69. Two fliC genes, flIC-53 and fliC-54, are nonfunctional owing to the insertions of IS1 and IS1222, respectively. The flkA and flmA regions are located in the 3' end of the rnpB gene and near the nlpA gene, respectively. Each of them is followed by a gene homologous to fljA, which is known to repress the expression of fliC(i) in Salmonella enterica serovar Typhimurium. These results suggest that they are derived from the same origin of the fljBA operon. However, these regions contain neither the hin gene nor the invertible H segment. The four flagellin genes, fliC16, flkA3, flkA53 and flmA54, share high homology in nucleotide and amino-acid sequences with one another and with the S. enterica serovar Typhimurium flagellin genes. The promoter sequence of fliC16 is homologous to that of fliC(i), whereas the promoter sequences of flkA and flmA are homologous to that of fljB. The terminator sequences of the fliC16, fliC-53 and fliC-54 genes are conserved among themselves and identical with that of the E. coli fliC48 gene. Three FljA repressors, FljA3, FljA53 and FljA54, are homologous highly with one another and moderately with FljA of Salmonella. These results indicate that six flagellin genes analyzed are markedly similar to the Salmonella flagellin genes, suggesting their lateral transfer from Salmonella.