title: Conformation of DNA modified with a dihydrodiol epoxide derivative of benzo[a]pyrene.
abstract: The conformation of calf thymus DNA modified by reaction with (+/-)-7beta,8alpha-dihydroxy-9alpha,10alpha-epoxy7,8,9,10-tetrahydrobenzo[a]pyrene, which binds covalently mainly to the 2-amino group of guanosine residues, was studied. With samples in which 1.5 or 2.2% of the bases were modified, there was a slight decrease in Tm during heat denaturation and a slight increase in susceptibility to the single strand specific nuclease S1. In a DNA sample in which 4.5% of the bases were modified, there was an appreciable decrease in Tm and a marked increase in susceptibility to S1 nuclease. The kinetics of the reaction of the modified DNAs with formaldehyde provided evidence for locally destabilized regions ranging from 1 to 7 base plates, depending on the extent of modification. Alkaline and neutral sucrose gradient analyses revealed no evidence for strand breakage in the 1.5 and 2.2% modified samples, although single-strand breaks were found in the 4.5% modified samples. Taken together, these results suggest that DNA molecules containing a covalently bound benzo[a]pyrene derivative have an altered conformation characterized by small localized regions which are destabilized and easily denatured. The conformational changes associated with the covalent binding of the benzo[a]pyrene derivative to native DNA appear to be different from, and less marked, than those associated with the covalent binding of N-2-acetylaminofluorene to native DNA.
mesh_terms: D000818:Animals; D001580:Benzopyrenes / Q000494:pharmacology*; D002417:Cattle; D004247:DNA; D003851:Deoxyribonucleases; D004988:Ethers, Cyclic / Q000494:pharmacology; D005557:Formaldehyde; D006358:Hot Temperature; D007700:Kinetics; D009690:Nucleic Acid Conformation / Q000187:drug effects*; D009691:Nucleic Acid Denaturation; D013950:Thymus Gland
chemical_list: D001580:Benzopyrenes; D004988:Ethers, Cyclic; D005557:Formaldehyde; D004247:DNA; D003851:Deoxyribonucleases