Transcription of chromatin by an RNA polymerase of calf thymus which is sensitive to high concentrations of alpha-amanitin.

RNA polymerase which is sensitive to high concentrations of α-amanitin has been obtained by low-salt extraction of whole calf thymus tissue. Some characteristics of this Form III-type polymerase have been compared with Form II. Both enzymes require a higher concentration of purine nucleoside triphosphates compared to pyrimidine nucleoside triphosphates. The Form III-type polymerase is larger than Form II. It transcribes native DNA better than denatured DNA and transcribes chromatin efficiently. Under various salt and metal conditions Form II transcribes native DNA and chromatin poorly relative to denatured DNA. These results suggest that Form III RNA polymerase is a useful enzyme with which to study the transcription of chromatin in vitro and may possess some factor (which Form II lacks) which is necessary for transcription of double-stranded templates.