Flagellar switch of Salmonella typhimurium: gene sequences and deduced protein sequences

Abstract

The fliG, fliM, and fliN genes of Salmonella typhimurium encode flagellar components that participate in energy transduction and switching. We have cloned these genes and determined their sequences. The deduced amino acid sequences correspond to proteins with molecular masses of 36,809, 37,815, and 14,772 daltons, respectively. None of the protein sequences are especially hydrophobic or look as though they correspond to integral membrane proteins, a result consistent with other evidence suggesting that the proteins may be peripheral to the membrane, possibly mounted onto the basal body M ring. The fliL gene, which immediately precedes fliM, is of unknown function; it encodes a protein with a deduced molecular mass of 17,082 daltons. The hydropathy profile of FliL indicates that it is likely to be an integral membrane protein with at least one spanning segment, near its N terminus. None of the four proteins exhibit consensus N-terminal signal sequences. Comparison of the fliL, fliM, and fliN sequences with the homologous ones in Escherichia coli reveals ranges of similarities of 77 to 95% at the amino acid level and 75 to 86% at the nucleotide level, with the majority (58 to 89%) of codon changes being synonymous ones.