Changes in ribonucleases during differentiation (spherulation) of Physarum polycephalum

Growth and differentiation of the water mold Blastocladiella emersonii: cytodifferentiation and the role of ribonucleic acid and protein synthesis.

“…46) (138,150,227). Actinomycin D (5 to 25 ug/ml) inhibits this incorporation by more than 98% with-out blocking encystment or germ tube formation until 45 (Lovett and Wilt, unpublished data). This means that, like protein synthesis, RNA synthesis is started up in a short period between 10 and 15 min during the maximum rise in zoospore encystment.…”

“…Significant losses in RNA (45) and increased ribonuclease levels (46) also accompany differentiation in Physarum. Turnover is indicated by the increased specific activity of RNA in the presence of [3H]uridine, despite the losses in total RNA (45), and by the decrease in specific activity of prelabeled RNA during differentiation (47). However, problems of precursor permeation and the failure of actinomycin D to block more than 80% ofthe uridine incorporation during differentiation (45, 203) make it difficult to interpret the results of the studies of RNA synthesis and the rates of turnover in Physarum.…”

“…However, problems of precursor permeation and the failure of actinomycin D to block more than 80% ofthe uridine incorporation during differentiation (45, 203) make it difficult to interpret the results of the studies of RNA synthesis and the rates of turnover in Physarum. All classes of RNA do appear to be made at a low rate in both spherulation and sporulation (45,47,203,204), and hydridization-competition experiments indicate that some ofthe RNA synthesized during differentiation may differ from the growth phase (45,47,203,204). However, the function, if any, of the putative new or unique RNA transcripts has not been demonstrated, although some candidates have been suggested for their translation products, e.g., spore wall proteins (122) and acid nuclear proteins (143).…”