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Solution conformation and mutagenic specificity of 1,N6-ethenoadenine
A K Basu1, J M McNulty, W G McGregor
1Department of Chemistry, University of Connecticut, Storrs 06269, USA.
IARC Scientific Publications
|January 8, 2000
Summary
Etheno adducts like 1,N6-ethenoadenine (epsilon A) and 3,N4-ethenocytosine (epsilon C) are mutagenic, with varying effects across species and DNA conditions. Their mutagenic mechanisms involve specific base substitutions and DNA polymerase interactions.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- Three etheno adducts (1,N6-ethenoadenine (epsilon A), 3,N4-ethenocytosine (epsilon C), and N2,3-ethenoguanine (N2,3-epsilon G)) are known mutagens.
- Mutagenicity varies between adducts and is influenced by DNA strand and cellular repair mechanisms.
Purpose of the Study:
- To investigate the mutagenic potential and mechanisms of etheno adducts in different cellular systems.
- To elucidate the role of DNA polymerase and cellular repair in processing these adducts.
Main Methods:
- Site-specific introduction of etheno adducts into DNA.
- Mutation frequency analysis in Escherichia coli and simian kidney cells.
- Effect of UV irradiation and DNA polymerase deficient mutants on mutagenicity.
- Nuclear magnetic resonance (NMR) spectrometry to study base pairing.
- In vitro replication assays using human cell extracts.
Main Results:
- Epsilon C is significantly more mutagenic than epsilon A in E. coli, with enhanced mutagenicity after UV irradiation or in exonuclease-deficient cells.
- Epsilon A primarily causes A-->G transitions, while epsilon C causes C-->T and C-->A substitutions.
- Both epsilon A and epsilon C are potent mutagens in simian kidney cells, inducing predominantly transitions (epsilon A-->G) and transversions (epsilon C-->A), respectively.
- NMR studies reveal stabilized, yet syn-aligned, base pairs for epsilon C, influencing DNA synthesis.
- In vitro replication with human extracts shows epsilon A predominantly induces A-->G transitions.
Conclusions:
- Etheno adducts exhibit differential mutagenicity and mutation patterns in prokaryotic and eukaryotic cells.
- Cellular factors like UV-inducible proteins and proofreading exonuclease activity modulate the mutagenic outcome of etheno adducts.
- The conformation of etheno adducts, particularly their syn alignment, plays a critical role in DNA polymerase bypass and mutagenicity.