In living cells, polycyclic aromatic hydrocarbons (PAH), a well known class of environmentally ubiquitous chemical carcinogens, are metabolically activated to chemically highly reactive diol epoxide derivatives.It is well established that these compounds bind to DNA, thus giving rise to a variety of genotoxic effects, including mutations. The stereoisomeric bay region diol epoxides of benzo(a)pyrene (BPDE) and the fjord region diol epoxides benzo(c)phenanthrene are of additional great interest because BPDE binds predominantly to guanine residues in DNA, while B(c)PhDE also binds strongly to adenine residues. Furthermore, B(c)PhDE is a strong mammary carcinogen, while BPDE is much less active in this organ.
The specific aims of this study are to gain a detailed understanding of the relationships between (1) the mutagenic activities of these two PAH diol epoxides in vitro and in vivo, (2) the extent and characteristics of DNA damage and structural deformation induced by their covalent binding to guanine and adenine residues in DNA, (3) the conformational properties of the DNA adducts formed, (4) the structural and functional factors that distinguish lesions in known hotspots of mutation from lesions situated in inactive DNA sequences, and (5) the differences in all of these factors associated with biological activities of highly active and less active BPDE and B(c)PhDE stereoisomers. Chemically defined PAH diol epoxide-oligonucleotide adducts, with precisely positioned PAH moieties in a mutation hotspot and other DNA sequences, with distinct trans- or cis-N2-guanine and N6- adenine adduct stereochemistry, will be synthesized for site-directed mutagenesis studies in vivo and in vitro. The characteristics of these modified DNA sequences, will be studied by high resolution NMR, low- resolution optical spectroscopic techniques, and X-ray crystallographic diffraction techniques; deformations in the DNA structure at or near the site of the lesion, as well as formation of bends and hinge joins at the site of the lesions, will be investigated by high-resolution gel electrophoresis mobility retardation techniques.
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