GUANINE-SPECIFIC DNA-REPAIR AFTER TREATMENT OF MOUSE SKIN CELLS WITH N-METHYL-N'-NITRO-N-NITROSOGUANIDINE

  • 1 January 1976
    • journal article
    • research article
    • Vol. 36  (7) , 2321-2325
Abstract
The incorporation of [3H]thymidine and [3H]deoxyguanosine into DNA was studied during DNA repair in mouse skin cells treated with the skin tumor initiator N-methyl-N''-nitro-N-nitrosoguanidine. At high, toxic levels of N-methyl-N''-nitro-N-nitrosoguanidine, repair (incorporation of the precursor into DNA which had not replicated) was demonstrated with both precursors. At lower, less toxic doses of the carcinogen, repair could not be demonstrated with [3H]thymidine, but it was clearly demonstrable with [3H]deoxyguanosine. Two kinds of DNA repair, 1 in which a single base (in this case, guanine) replaces a base lost by chemical or enzymatic depurination and the 2nd in which more than 1 base is replaced, indicating synthesis of longer stretches of DNA after extensive enzymatic excision were observed. The guanine-specific repair shown at relatively nontoxic dose levels of N-methyl-N''-nitro-N-nitrosoguanidine may be more relevant to the survival of cells than the repair demonstrated with [3H]thymidine at higher doses.

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