title: DNA replication-blocking properties of adducts formed by aflatoxin B1-2,3-dichloride and aflatoxin B1-2,3-oxide.
abstract: The carcinogen aflatoxin B1 (AFB1), upon activation to a hypothesized AFB1-2,3-oxide (AFB1-oxide), reacts with DNA guanines. Aflatoxin B1-2,3-dichloride (AFB1-Cl2) was originally synthesized as an electronic analog for the putative AFB1-oxide, which has never been isolated due to presumed reactivity. We have previously shown that AFB1-oxide reacts with base-paired DNA guanines in a sequence-specific manner, as revealed by an alkali-degradation analysis. On the basis of a replication-block analysis, we have shown that AFB1-Cl2 reacts with single-stranded DNA preferentially at inverted repeat sequences, which were suggested to be capable of forming intrastrand base-paired structures. Here, we present data to show the following. Both AFB1-oxide and AFB1-Cl2 react with guanines in double-stranded DNA to induce similar sequence-specific, alkali-labile sites. Reactivity with partial DNA duplexes as well as the use of single-strand specific chemical probes directly demonstrates that AFB1-Cl2, like AFB1-oxide, prefers base-paired guanines over non-base-paired guanines. DNA replication block patterns induced by AFB1-oxide are essentially similar to those induced by AFB1-Cl2. Unexpectedly, and unlike other tested DNA lesions, Mn2+ does not appear to affect the template blocking properties of the adduct formed by AFB1-Cl2 or AFB1-oxide. The sites for replication stoppage as well as the lack of a Mn2+ effect on adducted templates have implications for the mechanisms of mutagenesis by activated AFB1.
mesh_terms: D016604:Aflatoxin B1 / Q000031:analogs & derivatives; D000348:Aflatoxins / Q000378:metabolism / Q000494:pharmacology*; D001482:Base Composition / Q000187:drug effects; D004247:DNA / Q000187:drug effects; D004249:DNA Damage; D004261:DNA Replication / Q000187:drug effects*; D004269:DNA, Bacterial / Q000187:drug effects; D004277:DNA, Single-Stranded / Q000187:drug effects; D004279:DNA, Viral / Q000187:drug effects; D006147:Guanine / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism; D008345:Manganese / Q000378:metabolism; D009690:Nucleic Acid Conformation / Q000187:drug effects; D012091:Repetitive Sequences, Nucleic Acid / Q000187:drug effects
chemical_list: D000348:Aflatoxins; D004269:DNA, Bacterial; D004277:DNA, Single-Stranded; D004279:DNA, Viral; C006426:aflatoxin B1-2,3-oxide; D008345:Manganese; D006147:Guanine; D004247:DNA; D016604:Aflatoxin B1; D008274:Magnesium