Mass spectrometric sequencing of site-specific carcinogen-modified oligodeoxyribonucleotides containing bulky benzo[a]pyrene diol epoxide deoxyguanosyl adducts

Site-specific carcinogen-modified oligonucleotides are often used in site-d irected mutagenesis and other biological and biochemical studies of structu re-function relationships. Postsynthetic analysis and confirmation of the s ites of carcinogen binding in such oligonucleotides is an important step in the characterization of these site-specific carcinogen-DNA adducts. It is shown here that negative ion mode electrospray tandem mass spectrometry met hods and collision-induced dissociation offer a rapid and convenient approa ch for the sequencing of products derived from the reaction of the carcinog enic and mutagenic metabolite of benzo[a]pyrene, the diol epoxide r7, t8-di hydroxy-t9, 10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti-BPDE), with th e 11-mer oligonucleotide d(CATGCGGCCTAC). The site of reaction of anti-BPDE with either one of the three dG residues in this oligonucleotide can be ac curately established by comparing the mass/charge ratios of the observed co llision-induced dissociation fragments with calculated values. (C) 1998 Aca demic Press.