Molecular analysis of Salmonella hisG428 ochre revertants for rapid characterization of mutational specificity

The Salmonella typhimurium tester strains TA104 and TA102 were developed primarily to aid in the detection of oxidative mutagens and other agents that react preferentially with AT base pairs. Reversion of prototrophy of strains harboring the hisG428 ochre allele can occur by (i) any of seven single base substitutions or (ii) several tandem double base substitutions at the ochre codon, (iii) in-frame deletions removing all or part of the ochre codon or (iv) mutations at several distinct tRNA extragenic suppressor loci. We have used allele-specific oligonucleotide probes and DNA sequence analysis to characterize 625 revertants of strain TA104 (hisG428, rfa, DeltauvrB/pKM101) arising spontaneously or after treatment with methyl methane-sulfonate, glyoxal, streptonigrin or angelicin with UVA radiation. The reversion profiles obtained from these analyses distinguished readily each of the mutagen-treated populations from one another and from spontaneously derived revertants. Both GC and AT base pair-specific revertants were observed. Molecular analyses of S. typhimurium hisG428 revertants permitted rapid assessment of base pair substitution specificity of mutagens, especially the detection of AT base pair substitutions not recovered in strains carrying the complementary hisG46 allele.