Mutational consequences of replication of M13mp7L2 constructs containing cis-opened benzo[a]pyrene 7,8-diol 9,10-epoxide-deoxyadenosine adducts

The four adducts that arise by cis ring opening of the four optically activ e benzo[a]pyrene diol epoxides by the exocyclic N-6-amino group of deoxyade nosine were incorporated synthetically into each of two different oligonucl eotide 16-mers, 5'-TTTXGAGTCTGCTCCC-3' [context I(A)] and 5'-CAGXTTTAGAGTCT GC-3' [context, II(A)], at the X position. The eight resultant oligonucleot ides were separately ligated into bacteriophage M13mp7L2 and replicated in Escherichia coli that had been SOS-induced, and the progeny were analyzed t o evaluate the consequences of replication past these adducts. The presence of these adducts reduced plaque yields substantially However, the progeny obtained exhibited high frequencies of base substitution mutation ranging f rom 9 to 68%, depending upon the individual adduct and the sequence context in which it was placed. For most of the adducts, A --> T transversion was the mutation found most, frequently in either sequence context, and mutatio n frequencies in context I(A) were always substantially greater than those in context II(A). In context I(A), adducts with an R configuration at the s ite of nucleoside attachment were more mutagenic than those with an S confi guration. In both sequence contexts that were studied, the cis adduct arisi ng from the (7S,8R)-diol (SS,10R)-epoxide was the most mutagenic adduct. Th ese findings clearly show that individual mutation frequencies are determin ed by the combined effects of both adduct; structure and sequence context.