Isolation and characterization of the RNA of membrane-bound ribosomes in Dictyostelium discoideum.

The RNA of membrane-bound ribosomes, isolated from Dictyostelium discoideum, represented 13 to 16% of the total ribosomal RNA (rRNA) present throughout growth and development. Membrane-bound ribosomes were released by treatment with sodium deoxycholate and Brij 58. There were no obvious differences in size and base composition between RNAs derived from membrane-bound or free ribosomes. The 17S membrane-bound rRNA and free rRNAs appeared to have similar methyl contents. However, the 25S membrane-bound rRNA contained about 16 to 20% fewer methyl groups than the 17S membrane-bound rRNA and free rRNAs. Free rRNAs turned over rapidly during early development but not during the disaggregation and reaggregation processes. Membrane-bound rRNAs showed very little turnover during the early stages of morphogenesis, but showed rapid turnover during the late stages of development; this class of rRNAs did not turn over during early stages of reaggregation but turned over rapidly during later stages of reaggregation.