STEREOCHEMISTRY-DEPENDENT BENDING IN OLIGONUCLEOTIDE DUPLEXES INDUCEDBY SITE-SPECIFIC COVALENT BENZO[A]PYRENE DIOL EPOXIDE-GUANINE LESIONS

The apparent persistence length of enzymatically linearized pIBI30 pla smid DNA molecules similar to 2300 bp long, as measured by a hydrodyna mic linear flow dichroism method, is markedly decreased after covalent binding of the highly tumorigenic benzo[a]pyrene metabolite 7R,8S-dih ydroxy-9S,10Repoxy-7,8,9, 10-tetrahydrobenzo[a]pyrene [(+)-anti-BPDE]. In striking contrast, the binding of the non-tumorigenic, mirror-imag e 7S,8R,9R,10S enantiomer [(-)-anti-BPDE] to DNA has no measurable eff ect on its alignment in hydrodynamic flow gradients (less than or equa l to 2.2% of the DNA bases modified). In order to relate this effect t o BPDE-nucleotide lesions of defined stereochemistry, the bending indu ced by site-specifically placed and stereochemically defined (+)- and (-)-anti-BPDE-N-2-dG lesions In an 11mer deoxyoligonucleotide duplex w as studied by ligation and gel electrophoresis methods. Out of the fou r stereochemically isomeric anti-BPDE-N-2-deoxyguanosyl (dG) adducts w ith either (+)-trans, (-)-trans, (+)-cis, and (-)-cis adduct stereoche mistry, on ly the (+)-trans adduct gives rise to prominent bends or fl exible hinge joints In the modified oligonucleotide duplexes. Since bo th anti-BPDE enantiomers are known to bind preferentially to dG (great er than or equal to 85%), these observations can account for the diffe rences in persistence lengths of DNA modified with either (+)-anti-BPD E or the chiral (-)-anti-BPDE isomer.