Modification of DNA by aflatoxin B1 creates alkali-labile lesions in DNA at positions of guanine and adenine.

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Abstract
The damage to DNA by the hepatocarcinogen aflatoxin B1 was investigated. A DNA fragment of known sequence of the lactose promoter-operator region used as a substrate for modification by aflatoxin B1. The DNA was incubated with aflatoxin B1 in crude mammalian liver extracts or with purified rat liver microsomes. Treatment of the DNA incubated in the complete system with either 1 M piperidine or 0.1 M NaOH at 90.degree. revealed alkali-labile lesions in the DNA. The exact location of the cleavage site was determined by comparison of the length of the cleavage products with the known sequence on polyacrylamide gels. The lengths of the cleavage products were the same as those produced by alkali-induced breakage of the same sequence of DNA that was modified with dimethyl sulfate. The major cleavage products of the aflatoxin B1-modified DNA were at positions of guanine and the minor cleavage products were at positions of adenine. Modification of DNA by aflatoxin B1 creates alkali-labile sites at positions of guanine and to a lesser extent adenine.