O6-Methylguanine-DNA methyltransferase activity and sensitivity to N-methyl-N'-nitro-nitrosoguanidine during human T-lymphocyte differentiation

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Abstract
The activity of O 6 -methylguanine-DNA methyltransferase (MT) was assayed in various human lymphoid cell populations. It was found that during T-cell differentiation the activity of MT increased from 7000 MT molecules in thymocytes to 31 000 MT molecules in mature T-lymphocytes. The number of MT molecules also increased 2- to 3-fold in the course of the cell division cycle but the specific activity of MT did not change significantly. T-cell tumors and T-cell lines contained a higher number of MT molecules (70 000–125 000 molecules/cell) compared to normal T-lymphocytes. The sensitivities of various lymphoid cells to the DNA methylating agent N -methyl- N '-nitro- N -nitrosoguanidine correlated well with MT activities observed in cell extracts.