Classification of aminotransferase (C gene) mutants in the histidine operon

Abstract

The mutants in the aminotransferase gene (C gene) of the histidine operon in Salmonella typhimurium have been subdivided into nonsense (amber and ochre), missense, and frameshift classes. The major criteria for this classification are mutagenesis, suppression data from amber and ochre suppressors, and phenotypic curing. The nonsense and frameshift mutants are polar; the missense mutants are nonpolar. Mutants made with 2-aminopurine were almost all either amber or ochre mutants. N-Methyl-N′-nitro-N-nitrosoguanidine induces the reversion of all but the frameshift mutants.