MUTATION SPECTRA OF 1,2-DIBROMOETHANE, 1,2-DICHLOROETHANE AND 1-BROMO-2-CHLOROETHANE IN EXCISION-REPAIR PROFICIENT AND REPAIR-DEFICIENT STRAINS OF DROSOPHILA-MELANOGASTER

DNA sequence changes produced by 1,2-dibromoethane (DBE), 1,2-dichloroethane (DCE) and 1-bromo-2-chloroethane (BCE) were analyzed using the vermilion locus of Drosophila melanogaster. Under excision repair proficient (exr(+)) conditions (mutagenized exr(+) males mated with exr(+) females) all mutants isolated from the first generation (F1) after DBE and DCE exposure represented DNA rearrangements (multilocus deletions, small deletions with tandem repeats, duplicate insertions). By contrast, mutants expressing a vermilion phenotype only in the M (F1 mosaics) all carried single bp changes. When exr(+) males, after exposure to DBE, were mated to excision repair deficient (exr(-)) mus 201 females 11 of 14 mutational events isolated from either F1 or F2 progeny were single bp changes. In general the mutation spectra for the three dihaloalkanes were similar to the spectrum obtained at the same locus for the direct-acting monofunctional agent methylmethanesulfonate (MMS). The data lend support to the conclusions that these 1,2-dihaloalkanes are genotoxic through modification at ring nitrogens in DNA, primarily at the N7 of guanine and, to a lesser extent, at the N1 of adenine. These N-adducts could be directly miscoding. However, more important for the mutagenic action of the chemicals seems to be the formation of non-coding lesions and/or misrepair.