SOME ASPECTS OF EMS-INDUCED MUTAGENESIS IN ESCHERICHIA-COLI

AB2497 and its mutS and umuDC derivatives were EMS-treated at the stat ionary phase and specificity of mutation measured. It was found that: (i) in mutS+ cells EMS induces predominantly GC --> AT transitions (by supB or supE(oc) formation) and in mutS- cells mainly AT --> TA trans versions (by supL(NG) formation); (ii) transversions of AT --> TA are umuDC-dependent and mutational specificity is biased towards AT --> GC transitions in muts umuDC strains. When mutS-umuDC- cells were transf ected with plasmids bearing umuD'C or umuDC genes, mutational specific ity was again biased towards AT --> TA transversions; (iii) experiment s with bacteria bearing umuC=lacZ or recA=lacZ fusions suggest that pr ocessing of UmuD --> UmuD' might be poorer in EMS-treated mutS- than i n mutS' cells.