Nitropyrenes, which form during diesel fuel combustion, cause mutations and are carcinogenic in some animals. Dr. Veronica Maher and colleagues at Michigan State University studied the effect of nitropyrene-DNA adducts on gene mutation. The investigators exposed a specific gene, in culture, to each of two nitropyrene derivatives. They then (1) compared the number of adducts formed by each derivative, (2) analyzed the chemical structure of the adducts, and (3) determined in which region of the DNA the adducts formed. To determine the relation between the location of DNA adducts and mutation, the investigators compared the regions in DNA where adducts formed to those regions where mutations occurred. In another series of experiments, the researchers exposed genes to nitropyrene derivatives to determine if nitropyrene-DNA adducts stimulated homologous recombination.