Genetic mapping of katG, a locus that affects synthesis of the bifunctional catalase-peroxidase hydroperoxidase I in Escherichia coli.

A locus unlinked to either katE or katF that affected catalase levels in Escherichia coli was identified and localized between metB and ppc at 89.2 min on the genome. The locus was named katG. Mutations in katG which prevented the formation of both isoenzyme forms of the bifunctional catalase-peroxidase HPI were created both by nitrosoguanidine and by transposon Tn10 insertions. All katG+ recombinants and transductants contained both HPI isoenzymes. Despite the common feature of little or no catalase activity in four of the catalase-deficient strains, subtle differences in the phenotypes of each strain resulted from the different katG mutations. All three mutants caused by nitrosoguanidine produced a protein with little or no catalase activity but with the same subunit molecular weight and with similar antigenic properties to HPI, implying the presence of missense mutations rather than nonsense mutations in each strain. Indeed one mutant produced an HPI-like protein that retained peroxidase activity, whereas the HPI-like protein in a second mutant exhibited no catalase or peroxidase activity. The third mutant responded to ascorbate induction with the synthesis of near normal catalase levels, suggesting a regulatory defect. The Tn10 insertion mutant produced no catalase and no protein that was antigenically similar to HPI.