Inducible Repair of Phosphotriesters in Escherichia coli

Extracts from Escherichia coli cells induced for the adaptive response have been prepared that are capable of repairing O6-methylguanine, O4-methylthymine, and the phosphotriesters produced on the DNA backbone by alkylating agents such as N-methyl-N′-nitro-N-nitrosoguanidine (MNNG). The phosphotriesters are repaired by a methyltransferase distinct from the one that demethylates O6-methylguanine. We propose that this increased capacity to repair phosphotriesters accounts for much of the increased resistance to MNNG toxicity seen in cultures induced for the adaptive response.