DNA sequence adjacent to flagellar genes and evolution of flagellar-phase variation

Abstract

A variety of factors, including phase variation, are involved in the regulation of flagellin gene expression in Salmonella sp. Flagellar-phase variation refers to the alternate expression of 2 different flagellin genes, H1 and H2. Site-specific inversion of a DNA segment adjacent to the H2 gene is responsible for switching expression. The segment includes the H2 promoter and the hin gene, which is required to mediate the inversion. Sequences in this region have homology with the corresponding sequences adjacent to the H1 flagellin gene in Salmonella sp. and the hag flagellin gene in Escherichia coli. The hin gene is also homologous to the gin gene, which is found on phage Mu. To understand gene expression and the origin of these relationships, the DNA sequence adjacent to all 3 flagellin genes was compared. The sequence data suggest a mechanism for the evolution of the hin-H2 locus.