THE FLAGELLIN N-METHYLASE GENE FLIB AND AN ADJACENT SEROVAR-SPECIFIC IS200 ELEMENT IN SALMONELLA-TYPHIMURIUM

The cloning and molecular genetic analysis of a locus mapping within t he flagellar gene (fli) complex of Salmonella typhimurium is reported. A copy of the insertion element IS200 was located in a noncoding stre tch of DNA upstream of the fliA gene. Comparative nucleotide sequence analysis showed that this copy of IS200 was 711 bp long and that its f lanking regions contained no features common to other characterized in sertion sites of this element. The element was located 37 bp downstrea m of an ORF whose product was shown by interspecific transfer and amin o acid analysis to carry out N-methylation of selected lysine residues in Salmonella flagellin. The sequence and phenotype of this ORF ident ified it as fliB, encoding the only prokaryotic N-methylase acting on amino groups to have been characterized to date. It was found to be co nserved among all clinically significant serovars of Salmonella. The I S200 insertion site is of particular interest since it was conserved i n all but two rare evolutionary lines of S. typhimurium, and was absen t from 85 Salmonella strains belonging to 37 other serovars. It is thu s a phylogenetically significant marker at the serovar level.