Identification of alkylation products of styrene oxide in single- and double-stranded DNA

Radioactive styrene oxide was reacted with double- and single-stranded DNA and the binding products were characterized by HPLC after neutral hydrolysis and enzyme digestion of DNA. More products were formed in single-stranded DNA as compared with double-stranded DNA. In single-stranded DNA at least 95% of the adducts were guanine N-7-,N2- and O6-alkylation products; they were formed in proportions 54:33:12. In double-stranded DNA the respective proportion was 74:23:3.7, indicating a selective suppression of alkylation at atoms N2 and, particularly, O6 that take part in hydrogen bonding in double-stranded DNA. The alpha- and beta-isomers of 7-alkylguanine were formed in a similar proportion in single- and double-stranded DNA, indicating no steric hindrance.