Synthesis of actinomycin-insensitive RNA during the first postirradiation mitotic cycle, in the synchronously mitotic plasmodia of Physarum polycephalum.

A sucrose density gradient analysis of 3H-uridine pulse-labelled RNA from the first postirradiation mitotic cycle of Physarum polycephalum shows that all the density classes of RNA synthesized during this period are resistant to the peptide-antibiotic, actinomycin D. In fact, the synthesis is found to be greater in the presence of the drug. The heterogenously sedimenting synthetic activity here may represent a single species of RNA and its precursors or more than one kind of RNA. Further characterization of this RNA is meaningful in view of the actinomycin insensitivity of the postirradiation mitotic cycle itself to this antibiotic.

Transcription in ultra violet-irradiated plasmodia of Physarum polycephalum.

In Physarum polycephalum, transcription is significantly inhibited for the whole of the ultra violet-induced, extended G2 phase. Although, there is some increase in the rate of transcription closer to the first post-irradiation mitosis, thereafter, ovrall synthesis continues to be low. Also, the plasmodia developed significant resistance to actinomycin D during this period. The resistance is both in terms of mitosis and RNA synthesis. The overall depression in transcription and the drug resistance are apparently related phenomena.