Porphobilinogen-accumulating mutants of Salmonella typhimurium LT2

Four independent porphobilinogen-accumulating mutants of Salmonella typhimurium LT2 were isolated by selecting for dwarf colony formation on neomycin agar media. Cell-free extracts of the parent strain, but not of the mutants, were able to convert 5-aminolaevulinic acid or porphobilinogen to porphyrins. The results indicated that the mutants were deficient in uroporphyrinogen I synthase (EC. 4.3.I. 8) activity: these are the first mutants of this type reported in S. typhimurium LT2. Mapping of the hemC locus (for uroporphyrinogen I synthase) by F-mediated conjugation and by P22-mediated transduction showed the gene sequence ilvEDAC-hemC-cya-metE.