The replication fate of R- and S-styrene oxide adducts on adenine N6 is dependent on both the chirality of the lesion and the local sequence context.

In order to deduce the biological fate of adducts formed by the reaction of styrene oxide, a suspected carcinogen, with DNA, four oligodeoxynucleotides were synthesized which contained either R- or S-styrene oxide lesions on the N6 position of neighboring adenines within the human N-ras codon 61. When these adducted oligodeoxynucleotides were ligated into the single-stranded vector M13mp7L2 and the modified DNA used to transform repair-deficient Escherichia coli, the resultant plaque-forming abilities were found to vary as much as 300-fold, depending on the stereochemical configuration of the styrene oxide lesion and the sequence context in the vicinity of the damage. The frequency of mutations caused by the various styrene oxide adducts were similarly dependent on both their chirality and local sequence context. Oligodeoxynucleotide templates bearing these same four adducts were also constructed in order to evaluate their replication in vitro by the Klenow fragment. Three of the four styryl-modified templates yielded significant levels of fully extended primer upon polymerization. In contrast, the template containing R-styrene oxide at the second position of N-ras 61 was a very poor substrate for replication, a result which correlates well with the observed lethality of this lesion in vivo.