CYCLE-DEPENDENT REMOVAL OF CERTAIN METHYLATED BASES FROM DNA OF 10T1-2 CELLS TREATED WITH N-METHYL-N'-NITRO-N-NITROSOGUANIDINE

  • 1 January 1981
    • journal article
    • research article
    • Vol. 41  (4) , 1373-1378
Abstract
The loss of N-methyl-N-nitro-N-nitrosoguanidine (MNNG) [carcinogen]-induced adducts from DNA was quantitated during the G1 and S phases of synchronously proliferating mouse 10T1/2 cells [mouse embryo fibroblast] exposed to MNNG (2 .mu.g/ml) when they were in confluence-induced arrest of proliferation or at the G1-S border. When treated at either time, N-7-methylguanine and O6-methylguanine were not excised from the template DNA during the subsequent S phase. Both lesions were efficiently removed during the G1 phase immediately following exposure to MNNG, and during the 2nd G1 phase after an S phase during which no loss occurred. N-3-methyladenine was lost rapidly during the G1 and S phases following MNNG treatment. N-7-Methylguanine and O6-methylguanine were removed from logarithmically growing cell populations more slowly than from cells passing synchronously through the G1 phase. When the observed rate of loss in logarithmic cultures was corrected for the fraction of the logarithmic population located in the S phase, the rates of loss of the 2 methylated bases were the same as those observed in the G1 phase in synchronous cultures.

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