Genetic Analysis of H2, the Structural Gene for Phase-2 Flagellin in Salmonella

Summary: For the mapping of H1, the structural gene for phase-1 flagellin in Salmonella, spontaneous non-flagellate H1 mutants were isolated from a phase-1 stable derivative, SJ925 H1-g1g2g3t, of Salmonella abortusequi. First, mapping was carried out with the deletion mutants among them by P22 phage-mediated transduction. Mutants of flaA1 and flaL, adjoining opposite sides of H1, were also included in the mapping. As the result, H1 was divided into 16 segments by 15 deletions. Mapping by recombination frequencies was then carried out using representative H1 mutants. Comparison of the two maps showed that 14 consecutive segments near flaL covered about 70% of the non-flagellate H1 mutational sites, although they were confined to a quarter of H1 in the recombination map. The other two segments were found to occupy the remaining three quarters of H1. By use of the deletion map, the sites of three phase-1 curly and three ah1 mutations were determined. The curly mutational sites were mapped in the segment second from the flaA1 side and the ahi mutational sites in the segments near the flaL side. To ascertain approximate positions of the areas determining the phase-1 antigen specificities, their arrangement relative to a curly mutational site, curly-2, and H1-linked fla genes was examined by three-point crosses. From the results, all the antigenic specificity-determining areas examined were located between flaA1 and curly-2 in the following order: flaA1--g2-g1-g4-(g3,g5,f,m,t)-curly-2---flaL.