title: Human diploid fibroblast mutants with altered RNA polymerase II.
abstract: Clones resistant to the cytotoxic action of alpha-amanitin have been isolated from a strain of fetal human lung diploid fibroblasts. Resistant clones were recovered at a frequencey of 5 X 10(-8) after single-step selections following mutagenesis with the mutagen ethyl methane sulfonate. Following propagation in drug-free medium, the clones retained the selected phenotype and in both growth and plating experiments showed a 10-50-fold higher resistance than wild-type cells to the cytotoxicity of 0.25 microgram/ml alpha-amanitin. The alpha-amanitin sensitivity of RNA polymerase II purified from the mutant cells suggests the presence of two forms of the enzyme, one similar to that found in wild-type cells and a second form with increased resistance to alpha-amanitin inhibition. These results are consistent with previous evidence that alpha-amanitin resistance behaves as a codominant marker in mammalian cells.
mesh_terms: D000546:Amanitins / Q000494:pharmacology; D002460:Cell Line; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism*; D004351:Drug Resistance; D005347:Fibroblasts / Q000201:enzymology; D005796:Genes; D005799:Genes, Dominant; D006801:Humans; D009154:Mutation; D012319:RNA Polymerase II / Q000378:metabolism*
chemical_list: D000546:Amanitins; D012319:RNA Polymerase II; D012321:DNA-Directed RNA Polymerases