Effect of alpha-amanitin and actinomycin D on RNA synthesis in the protoplasts of Aspergillus nidulans.

RNA synthesis was studied in protoplasts from Aspergillus nidulans, which remained metabolically active for several days under the appropriate conditions. It is concluded, that at certain actinomycin D concentrations the ribosomal RNA synthesis can be selectively inhibited. However, alpha-amanitin at concentrations up to 400 micrograms/ml neither influenced the total nor the RNA polymerase II directed RNA synthesis. It was possible to discriminate between the RNA polymerase I or II directed RNA synthesis due to the presence of poly(A) tails attached to at least part of the RNA, presumably messenger RNAs, or their precursors.