Suppression of human DNA alkylation-repair defects by Escherichia coli DNA-repair genes.

The ada-alkB operon protects Escherichia coli against the effects of many alkylating agents. We have subcloned it into the pSV2 mammalian expression vector to yield pSV2ada-alkB, and this plasmid has been introduced into Mer- HeLa S3 cells, which are extremely sensitive to killing and induction of sister chromatid exchange by alkylating agents. One transformant (the S3-9 cell line) has several integrated copies of pSV2ada-alkB and was found to express a very high level of the ada gene product, the 39-kDa O6-methylguanine-DNA methyltransferase. S3-9 cells were found to have become resistant to killing and induction of sister chromatid exchange by two alkylating agents, N-methyl-N'-nitro-N-nitrosoguanidine and N,N'-bis(2-chloroethyl)-N-nitro-sourea. This shows that bacterial DNA alkylation-repair genes are able to suppress the alkylation-repair defects in human Mer- cells.