RNA metabolsim during vegetative growth and morphogenesis of the cellular slime mold Dictyostelium discoideum

During vegetative growth of the cellular slime mold Dictyostelium discoideum, RNA is rapidly labeled by radioactive precursor and both the 25 S and the 17 S ribosomal RNA species appear in the cytoplasm 6–7 min after the onset of labeling. Thirty minutes after further incorporation of radioactive RNA precursors has been blocked, less than 10% of the label in RNA is associated with the nuclear fraction. After aggregation of the slime mold amoebae, RNA appears in the cytoplasm at a reduced rate, the small ribosomal subunit appearing in the cytoplasmic fraction more slowly than the larger ribosomal subunit. Some labeled RNA remains in the nuclei of developing cells long after the incorporation of ³H-uridine is blocked.