RELEASE OF N2,3-ETHENOGUANINE FROM CHLOROACETALDEHYDE-TREATED DNA BY ESCHERICHIA-COLI 3-METHYLADENINE DNA GLYCOSYLASE-II

The human carcinogen vinyl chloride is metabolized in the liver to reactive intermediates which form N2,3-ethenoguanine in DNA. N2,3-Ethenoguanine is known to cause G --> A transitions during DNA replication in Escherichia coli, and its formation may be a carcinogenic event in higher organisms. To investigate the repair of N2,3 -ethenoguanine, we have prepared an N2,3-etheno[C-14]guanine-containing DNA substrate by nick-translating DNA with [C-14]dGTP and modifying the product with chloroacetaldehyde. E. coli 3-methyladenine DNA glycosylase II, purified from cells which carry the plasmid pYN1000, releases N2,3-ethenoguanine from chloroacetaldehyde-modified DNA in a protein- and time-dependent manner. This finding widens the known substrate specificity of glycosylase II to include a modified base which may be associated with the carcinogenic process. Similar enzymatic activity in eukaryotic cells might protect them from exposure to metabolites of vinyl chloride.