In the first phase of a wide ranging, long-term investigation of the interactions of environmental toxicants with DNA, the mycotoxin aflatoxin B1 and structurally related compounds will be investigated. Aflatoxin contamination of foodstuffs is a pervasive problem, seen particularly acutely in under-developed tropical areas, but also of much concern in this country. The non-covalent interactions of aflatoxins with DNA will be investigated to delineate the sequence and conformational requirements of DNA to obtain efficient binding. In addition, the structural features of the aflatoxin molecule will be manipulated to establish the criteria for efficient binding. It is hoped that a rationale can be developed for the apparent sequence specificity of interaction with DNA and that a physical picture of this interaction can be obtained. Covalent interactions are the basis of aflatoxin's potent mutagenicity. The solution structures of these covalent adducts will be investigated, looking both at the initial cationic adduct of aflatoxin B1-epoxide with N-7 of guanosine and at the formamidopyrimidine (FAPY) derivative which arises by hydrolysis of the imidazole ring of guanine in the cationic adduct. NMR will be used as one of the major tools to investigate the orientation of the aflatoxin in the oligonucleotide complexes. Methodology to deuterate the bases and deoxyribose sugars selectively will be developed for use in assigning and interpreting complex HI NMR spectra of oligonucleotides. Incorporation of deuterium into specific sites in the oligonucleotides will be achieved via synthesis from appropriately deuterated mononucleotides. The methodology will also be used in future studies of interactions of benzo[a]pyrene and other environmental pollutants with DNA and will be of general value in investigations of drug-DNA interactions.
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