The covalent structure of the phase-1 flagellar filament protein of Salmonella typhimurium and its comparison with other flagellins.

In order to circumvent problems associated with direct chemical analysis of the phase-1 flagellar filament protein (flagellin) of Salmonella typhimurium, the covalent structure was determined by recombinant DNA procedures. The corresponding structural gene (H-1i) was cloned into plasmid pBR322 in a 4.3-kilobase fragment produced by EcoRI digestion of chromosomal DNA, and the nucleotide sequence of the region specifying the flagellar protein was determined. Comparison of the data obtained with the limited information available for other salmonellar flagellins supported the concept that both ends of the molecule are conserved in this genus. Additionally, a conservation of base sequence in the region of H-1 genes coding for the N-terminal end of flagellins was apparent, suggesting that this area may have an additional regulatory role. The i flagellin was found to be unrelated to proteins in the NBRF data base with the exception of other flagellins. The three flagellins which have been sequenced to date (those produced by Bacillus subtilis, Caulobacter crescentis, and phase-1 S. typhimurium) show homologies in amino acid sequence at both the N-terminal and C-terminal ends despite large differences in their total molecular weight, and comparison suggests that B. subtilis and Salmonella are more closely related to each other than either is to Caulobacter.