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Chemical carcinogens as frameshift mutagens: Salmonella DNA sequence sensitive to mutagenesis by polycyclic
Abstract:
Other investigators have shown that several polycyclic carcinogens are frameshift mutagens in Salmonella. Mutagenic potency of these compounds is assessed by ability to induce reversion of histidine-requiring frameshift mutants to prototrophy. One frameshift mutation in the histidinol dehydrogenase gene, hisD3052, is unusually sensitive to mutagenesis by certain polycyclic carcinogens. We find that the 3052 mutation is a - 1 deletion, probably loss of a G.C pair from a DNA repeat of [unk]. The polycyclic carcinogens tested (e.g., 2-nitroso-fluorene) revert 3052 by deleting a [unk] doublet from the DNA sequence [unk], which is close to the 3052 site. This rare mispairing-prone sequence represents the carcinogen-sensitive "hotspot" in 3052. The ICR compounds, noncarcinogenic intercalating agents, show a broader specificity of mutagenesis. Reversion with these mutagens occurs predominantly by two mechanisms: one identical to that of the polycyclic carcinogens, and the other by +1 additions in a third DNA tract narrowly separated from the 3052 site. The alkylating carcinogen N-methyl-N'-nitro-N-nitrosoguanidine appears to have a similar dual specificity. DNA base changes in 3052 revertants have been correlated with properties of histidinol dehydrogenase in crude extracts. This correlation of DNA base sequence with electrophoretic and other properties of the mutant proteins allows one to analyze easily the specificity of new mutagens that mutate this strain.
Insights
Certain polycyclic carcinogens act as frameshift mutagens, specifically targeting a sensitive DNA sequence in Salmonella. This study identifies a unique mutation hotspot that reveals mutagen specificity.
Area of Science:
- Molecular Biology
- Genetics
- Toxicology
Background:
- Polycyclic carcinogens are known frameshift mutagens in Salmonella.
- Mutagenic potency is assessed by reversion of histidine-requiring frameshift mutants.
- The hisD3052 mutation exhibits unusual sensitivity to certain polycyclic carcinogens.
Purpose of the Study:
- To characterize the specific DNA mutation at the hisD3052 locus.
- To elucidate the mutagenic mechanisms of polycyclic carcinogens, ICR compounds, and N-methyl-N extquotesingle-nitro-N-nitrosoguanidine at this site.
- To correlate DNA sequence changes with protein properties for mutagen specificity analysis.
Main Methods:
- DNA sequencing to determine the nature of the hisD3052 mutation.
- Analysis of reversion events induced by various mutagens (polycyclic carcinogens, ICR compounds, N-methyl-N extquotesingle-nitro-N-nitrosoguanidine).
- Correlation of DNA base changes in revertants with electrophoretic and other properties of the mutant histidinol dehydrogenase protein.
Main Results:
- The hisD3052 mutation is a -1 deletion, likely involving the loss of a G.C pair from a DNA repeat.
- Polycyclic carcinogens revert hisD3052 by deleting a specific DNA doublet at a carcinogen-sensitive hotspot.
- ICR compounds and N-methyl-N extquotesingle-nitro-N-nitrosoguanidine exhibit dual mutagenic specificities, involving both deletion and +1 addition mechanisms at distinct DNA sequences.
Conclusions:
- A specific DNA sequence near the hisD3052 mutation acts as a hotspot for certain carcinogens.
- Mutagenesis mechanisms vary, with polycyclic carcinogens targeting a deletion hotspot, while other mutagens employ broader strategies.
- The hisD3052 system provides a sensitive platform for analyzing mutagen specificity by correlating DNA changes with protein alterations.