Complementation of sensitivity to alkylating agents in Escherichia coli and Chinese hamster ovary cells by expression of a cloned bacterial DNA repair gene.

Dual expression vectors derived from pSV2gpt and encoding all or part of the Escherichia coli ada+ gene have been constructed. Following transformation into an E. coli ada strain or transfection and stable integration into the genome of Chinese hamster ovary (CHO) cells, plasmid vectors containing the whole ada+ gene conferred resistance to both killing and mutagenesis by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Thus, the bacterial DNA repair gene was functionally expressed in the mammalian cells. Plasmids containing an N-terminal fragment of the ada+ gene which encoded only one of the two methyltransferase activities of the Ada protein did not significantly protect E. coli or CHO cells against MNNG. These results are consistent with the central role of the intact ada+ gene in controlling the adaptive response to alkylating agents in E. coli. However, the data further suggest that some alkylation lesions in DNA, such as O6-methylguanine, may exert partly different biological effects in E. coli and mammalian cells.