ALPHA-AMANITIN-RESISTANT D-MELANOGASTER WITH AN ALTERED RNA POLYMERASE-II

Following EMS mutagenesis we recovered a mutant of D. melanogaster that grows at concentrations of α-amanitin lethal to wild-type. To our knowledge this mutant represents the first example of an amanitin-resistant eucaryotic organism. The amanitin resistance of the mutant (AmaC4) is due to an alteration in its DNA-dependent RNA polymerase II, which is approximately 250 times less sensitive to inhibition by amanitin than the wild-type polymerase II whether tested in nuclei, in partially-fractionated extracts or as a highly purified enzyme. While the wild-type enzyme activity is inhibited 50% by 2.1 × 10-8 M α-amanitin, inhibition of 50% of the AmaC4 RNA polymerase II activity requires a toxin concentration of 5.6 × 10-6 M. The mutation responsible for the amanitin resistance of AmaC4 is on the X chromosome near the vermillion locus. © 1979.