Laser Pulse-Induced Photochemical Strand Cleavage of Site-Specifically and Covalently Modified (+)-anti-Benzo[a]pyrene Diol Epoxide-Oligonucleotide Adducts

Bin Li, Bing Mao, Tong Ming Liu, Jing Xu, Alexander Dourandin, Shantu Amin, Nicholas E. Geacintov

Research output: Contribution to journalArticle

Abstract

The specificity of the laser pulse-induced photocleavage method [Boles, T. C., and Hogan, M. E. (1986) Biochemistry 25, 3039] for detecting the sites of covalent binding of benzo[a]-pyrene diol epoxide in DNA was investigated using site-specifically modified oligonucleotide duplexes d(CTCACAT[G*]TACACTCT)•d(GAGAGTGTACATGTGA), where [G*] is the adducted guanine residue (+)-trans-anti-BPDE-N2-dG (anti-BPDE = 7β,8α-dihydroxy-9α,10α-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene). The appropriate oligonucleotide strands were 32P-end-labeled, and the duplexes were irradiated with a pulse train of 355 nm Nd:YAG laser pulses (~300 mW/cm2). The products of the photocleavage reaction were analyzed by denaturing gel electrophoresis. The major observed products included the intact oligonucleotide strand that had lost the BPDE residue, and shorter oligonucleotide fragments arising from strand scission at the BPDE-modified guanine residue and at nearby flanking bases. Photocleavage at the BPDE-modified G is dominant (≈50 ± 5% of the sum of all of the shorter oligonucleotide fragments), and cleavage extends to at least 4 bases on the 5'-side, and 7 bases on the 3'-side of the BPDE-modified G residue; the probability of cleavage diminishes with increasing distance from the modified G residue. On the unmodified complementary strand, nonspecific strand cleavage is also observed, but the probability of cleavage is ≥20 times smaller than at the BPDE-modified G residue on the modified strand. The photocleavage method thus preferentially causes strand scission at the sites of BPDE modification, but the occurrence of strand cleavage with lower probabilities at neighboring sites is also significant.

Original languageEnglish (US)
Pages (from-to)396-402
Number of pages7
JournalChemical research in toxicology
Volume8
Issue number3
DOIs
StatePublished - Apr 1995

ASJC Scopus subject areas

  • Toxicology

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