Expression in mammalian cells of a truncated Escherichia coli gene coding for O6-alkylguanine alkyltransferase reduces the toxic effects of alkylating agents.

The lesion O6-alkylguanine (O6-AG) is produced in cellular DNA following exposure to monofunctional alkylating agents and its miscoding and mutagenic properties have been demonstrated in specific in vitro systems. In order to examine whether this lesion could be responsible for any of the biological effects of alkylating agents in mammalian cells, we have constructed a plasmid containing the O6-AG alkyltransferase (ATase) region of the gene from Escherichia coli, the product of which normally repairs both O6-AG and alkylphosphotriesters in DNA. We have transfected the construction into Chinese hamster fibroblasts which are deficient in endogenous ATase activity and selected a clone that expresses the truncated repair gene. We demonstrate that this protein is functional, acts on damage in host cell DNA and protects the cells from the toxic effects of those alkylating agents that react extensively at oxygen atom positions.