Target sequences for mutagenesis in Salmonella histidine‐requiring mutants

Abstract Nucleotide target sequences involved in reversion to the wild type phenotype are diagrammed for Salmonella frameshift histidine‐requiring mutants hisD3052, hisD3018, hisD6610 , and hisD6580 and for base‐substitution mutants hisG46 and hisG428 . Frameshift strain hisC3076 probably reverts by nucleotide changes similar to those that occur during reversion of hisD3018 and hisD6610 . Multiple modes of reversion characterize each strain. Each strain also has a particularly diagnostic mutagen‐susceptible sequence. These highly mutagen‐susceptible stretches are the hisD3052 GCGCGCGC sequence, the hisD6610 CCCCCC sequence, the hisD6580 AAAAA sequence, and the A/T containing codon of hisG428 and G/C containing codon of hisG46 , respectively. Between them, hisG46 and hisG428 are reverted by all of the six possible base substitution transition and transversion mutations.