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Non-random alkylation of DNA sequences induced in vivo by chemical mutagens
1Dipartimento di Biologia delle Piante Agrarie, Università di Pisa, Italy.
Abstract:
Previous studies of the interaction of alkylating agents on the eukaryotic genome support the idea that induction of DNA adducts is at specific genomic sites. Here we show molecular and cytological evidence that alkylation is rather specific. Mammalian cell cultures were exposed to different doses of mutagens and the DNA was analyzed by density gradient ultracentrifugation, hydroxylapatite fractionation, and by restriction enzyme analysis. Studies with the labelled mutagens N-ethyl-N-nitrosourea and N-methyl-N'-nitro-N-nitrosoguanidine show that there is a non-random distribution of the adducts. The adducts are found more frequently in A-T, G-C rich satellite DNA and highly repetitive sequences. Analysis with restriction enzymes shows that both methyl and ethyl groups influence the restriction patterns of the enzymes HpaII and MspI that recognize specific endogenous DNA methylation. These data suggest, as a subsequent mechanism, a modification in the pattern of the normal endogenous methylation of 5-methylcytosine.
Insights
DNA alkylating agents show specific genomic interactions, not random. Adducts concentrate in repetitive DNA, altering methylation patterns, suggesting targeted genome modification by mutagens.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Previous research suggested alkylating agents induce DNA adducts at specific genomic sites.
- Understanding the precise distribution of DNA adducts is crucial for assessing mutagenic effects.
Purpose of the Study:
- To provide molecular and cytological evidence for the specificity of alkylation on the eukaryotic genome.
- To investigate the distribution patterns of DNA adducts induced by specific alkylating agents.
Main Methods:
- Mammalian cell cultures were treated with varying doses of mutagens.
- DNA analysis employed density gradient ultracentrifugation, hydroxylapatite fractionation, and restriction enzyme analysis.
- Labeled mutagens, N-ethyl-N-nitrosourea and N-methyl-N'-nitro-N-nitrosoguanidine, were used.
Main Results:
- Alkylation demonstrated a non-random distribution of DNA adducts.
- Adducts were found preferentially in A-T and G-C rich satellite DNA and highly repetitive sequences.
- Methyl and ethyl groups from mutagens influenced restriction enzyme patterns (HpaII, MspI), indicating altered endogenous DNA methylation.
Conclusions:
- Alkylation by these agents is specific, targeting repetitive DNA sequences.
- The observed changes suggest a modification in the endogenous methylation pattern of 5-methylcytosine as a downstream effect.
- These findings highlight a targeted mechanism of genome modification by alkylating agents.