The pattern of protein and nucleic acid synthesis in germinating spores of Phycomyces blakesleeanus

Summary Synthesis of proteins, RNA and DNA is measured by incorporation of labelled precursors at different times during germination of Phycomyces spores.RNA and protein synthesis increases immediately after activation. DNa synthesis begins at a later stage (± 8 h) of germination when germ tubes are already present. Nuclear division occurs earlier in germination (±4–5 h) and is accompanied by a decrease in RNA synthesis. It can be concluded that at least most of the dormant spores are in the G2 phase of the cell cycle.Analysis of ribosomal RNA after pulse-chase labelling shows only three labelled compounds: a precursor molecule (2.25×10⁶ daltons) and the two mature ribosomal RNA compounds (1.4×10⁶ and 0.7×10⁶ daltons). This suggests that the two rRNAs are formed directly from the precursor molecule. Cycloheximide totally blocks the transformation of the ribosomal precursor molecule into mature rRNA.