Genetic analysis of aromatic mutants of Salmonella typhimurium.

A N aromatic (aro) mutant of Escherichia coli may demand for its growth tyrosine, phenylalanine, tryptophan, para-aminobenzoic acid, para-hydroxybenzoic acid and a sixth unknown factor, or only the first two, three, four or five of these (DAVIS 1952a). Biochemical analyses of the aromatic pathway by several workers have indicated the possible presence of seven sequential steps leading to chorismic acid biosynthesis in E. coli (UMBARGER and DAVIS 1962; GIBSON and GIBSON 1964). Chorismic acid is then converted to the above aromatic end products by individual pathways (COTTON and GIBSON 1965; Cox and GIBSON 1964; GIBSON 1964; GIBSON, GIB~ON and Cox 1964). The genetic analysis of 89 aromatic mutants of Salmonella typhimurium presented here has shown that they represent mutations in five structural genes involved in chorismic acid biosynthesis. The mutants of each gene consist of those which require for growth two, three, four or five of the aromatic acids, as is the case in E. coli aro mutants (DAVIS 1952a; PITTARD and WALLACE 1966); also the variety of requirements among allelic mutants is related to mutational position within an aromatic gene. In addition to the aro mutants, phenylalanine-specific (phe) and tyrosine-specific ( t y r ) mutants were examined; only one locus was found for each of these classes.