Regulation of RNA polymerase II activity in a mutant rat myoblast cell line resistant to α amanitin

Abstract

A MUTANT cell line, Ama102, resistant to the cytotoxic effects of a amanitin, the specific inhibitor of RNA polymerase II (refs 1 and 2), has been selected³ from cultures of Yaffe's⁴ rat skeletal muscle myoblast cell line, L₆, treated with mutagen. Ama102 cells have similar doubling times for growth in the absence or presence of 3 μg ml⁻¹ α amanitin whereas the Ama⁺ parent does not survive in this concentration of α amanitin. Studies in vitro (ref. 3 and D.S. et al., manuscript in preparation) indicate that Ama102 cells possess an RNA polymerase II which, retains about 30% of its activity in 0.1 μg ml⁻¹ α amanitin, a concentration sufficient to inactivate completely the Ama⁺ polymerase II. If α amanitin has a similar inhibitory action in vivo and in vitro, the normal growth of Ama102 cells in α amanitin coupled with the partial resistance of its RNA polymerase II activity to α amanitin in vitro seems paradoxical. Does the mutant Ama102 cell grow normally in α amanitin with only 30% of its normal RNA polymerase II active, or can the RNA polymerase II activity increase when the mutant is grown in α amanitin? The experiments reported here indicate that Ama102 cells can compensate for the partial inactivation of RNA polymerase II by α amanitin by increasing the RNA polymerase II activity.