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Nucleosome structure modulates benzo[a]pyrenediol epoxide adduct formation
B D Thrall1, D B Mann, M J Smerdon
1Biology and Chemistry Department, Pacific Northwest Laboratory, Richland, Washington 99352.
Biochemistry
|March 1, 1994
Summary
Nucleosome structure, formed by DNA and histone octamers, impacts chemical carcinogen binding. DNA within nucleosomes shows suppressed adduct formation by benzo[a]pyrenediol epoxide (BPDE) at specific sites.
Area of Science:
- Biochemistry
- Molecular Biology
- Genetics
Background:
- Chemical carcinogens can form covalent adducts with DNA.
- Nucleosomes are the basic structural units of DNA packaging, influencing DNA accessibility.
- Understanding DNA-carcinogen interactions within nucleosomes is crucial for toxicology and cancer research.
Purpose of the Study:
- To investigate how nucleosome structure affects the formation of covalent DNA adducts by a chemical carcinogen.
- To determine the sequence and structural context of DNA modification within a reconstituted nucleosome.
Main Methods:
- Reconstitution of plasmid DNA with histone octamers to form nucleosomes.
- Digestion with micrococcal nuclease and hydroxyl radical footprinting to confirm nucleosome structure.
- Covalent adduct formation assay using benzo[a]pyrenediol epoxide (BPDE).
- Sequence-level adduction analysis via primer extension.
Main Results:
- Nucleosome formation altered the initial rate of BPDE adduct formation but not total adduction levels after 2 hours.
- Adduction within the 5S rRNA nucleosome was suppressed by approximately 50% compared to naked DNA.
- DNA sequences near the nucleosome dyad, exhibiting minor groove width modulations, were least susceptible to BPDE adduction.
Conclusions:
- Nucleosome structural features significantly influence the susceptibility of DNA to modification by chemical carcinogens like BPDE.
- DNA accessibility and specific structural motifs within nucleosomes dictate carcinogen binding sites.
- These findings highlight the protective role of nucleosome structure against DNA damage at certain sites.