Human mutant cell lines with altered RNA polymerase II.

A human fibrosarcoma cell line, HT-1080-6TG-9AM, resistant to alpha-amanitin at concentrations up to 10 micrograms/ml, was isolated after ethylmethanesulfonate mutagenesis and stepwise selection. The mutation is stable and dominant. RNA polymerase II purified from the mutant cells showed an altered affinity for labeled alpha-amanitin and the sensitivity of the enzyme to the fungal toxin was decreased 50- to 100-fold. This functional test demonstrated that the biochemical basis for the resistance of the cells to alpha-amanitin is due to an alteration of RNA polymerase II.