Characterization of Ribosomes in the Cellular Slime Mold, Dictyostelium discoideum

The sedimentation analysis of the ribosomes of Dictyostelium discoideum indicated that the monomeric ribosome had a sedimentation coefficient of about 83 S and could be dissociated into 61-S and 42-S ribosomal subunits. The 83-S ribosome contained 26-S and 17-S rRNA with a mass ratio of approximately 2:1. The 61-S ribosomal subunit contained 26-S rRNA and 4–5-S RNA, whereas the 42-S subunit contained only 17-S rRNA. When these subunits were suspended in 0.1 mM Mg2+ for a long period, treated with EDTA, or incubated with 0.5-M KC1, NaC1 or LiC1 in the presence in the presence of 0.1 mM Mg2+ for 1 hr, the sedimentation values of both subunits were decreased to a great extent. The small subunit was more sensitive to RNase [EC 2. 7. 7. 16] digestion than the large subunit. The electrophoretic analysis of basic proteins of ribosomes showed that the 61-S and 42-S subunit contained 21 and 18 components, respectively.