Mer- human cells, which lack O6-methylguanine DNA methyltransferase activity, are extremely sensitive to alkylation induced killing, mutation and sister chromatid exchange. We have analyzed a Mer+, a Mer-, and a Mer- revertant HeLa cell line and found that the methyltransferase deficiency correlates with increased levels of mutation and sister chromatid exchange, but does not correlate with increased killing of Mer- HeLa cells by alkylating agents. Furthermore, we show that HeLa Mer- cells repair N-3-methylguanine and N-3-methyladenine just as efficiently as HeLa Mer+ cells.
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Samson et al. (1987) studied this question.