Lowered induction of genetic tandem duplications in Salmonella by the pKM101 plasmid

Induction of genetic duplications and frameshift mutations in Salmonella typhimurium by acridines and acridine mustards: dependence on covalent binding of the mutagen to DNA

The aroC321 allele permits positive selection for the detection of a large genetic duplication that arises in the Salmonella typhimurium chromosome by homologous recombination. Strains that contain both aroC321 and the hisC3076 allele were constructed so that the induction of genetic duplications and frameshift mutations in a run of GC base pairs could be studied simultaneously by selecting for tryptophan and histidine prototrophy, respectively. Using these strains, we examined the ability of 9-aminoacridine, quinacrine, four acridine mustards (ICR-170, ICR-191, ICR-372, and quinacrine mustard) and the nitroacridine Entozon to induce genetic duplications and frameshift mutations. Although all these compounds induce reversion of hisC3076, only the four mustards and Entozon are effective as inducers of genetic duplications under identical treatment conditions. The induction of genetic duplications by acridine mustards, like the toxic and mutagenic effects of these compounds, is enhanced by a deficiency for excision repair caused by a deletion through the uvr B gene. The ineffectiveness of 9-aminoacridine and quinacrine in the test for genetic duplications indicates that simple intercalation is sufficient for the mutagenic effect measured with the hisC3076 allele but that the induction of duplications by the acridine mustards and Entozon requires covalent binding of the chemical to DNA.

Induction of genetic tandem duplications in Salmonella by polycyclic aromatic hydrocarbon and amine carcinogens

6 polycyclic aromatic hydrocarbon or similar amine carcinogens were tested as inducers of genetic tandem duplications in a rough strain of Salmonella typhimurium. When metabolically activated by rat-liver microsomes, all 6 were active in inducing genetic tandem duplications, yielding from over 3 times to almost 14 times as many tandem duplicants per viable bacterium as did concurrent uninduced control cultures. These results extend the number and chemical diversity of carcinogens shown to induce genetic duplications in bacterial tester systems. We suggest that polycyclic hydrocarbon carcinogens may act in carcinogenesis by inducing genetic duplications or other genetic rearrangements. Duplication induction may be a useful genetic endpoint for screening potential carcinogens.