Ribosomes of Brachionus plicatilis (Rotifera) – distribution in homogenate fractions and general properties

Abstract

(1) The content of DNA, RNA and of proteins of Brachionus plicatilis was estimated and the distribution of RNA and of proteins of different homogenate fractions characterised. (2) Ribosomes were isolated from Brachionus plicatilis homogenates and were characterised by gradient centrifugation. (3) Unlike the RNA content, the yield of ribosomes from different homogenate fractions is strongly dependent on the concentration of Mg²⁺-ions in the buffers. Likewise resuspension of ribosomes is more effective in Mg²⁺- (or Ca²⁺-) free buffers. (4) Dissociation of ribosomes was brought about by centrifugation of ribosomes in gradients containing less than 4 mM Mg²⁺. In this case, beside the peaks of subunits, a peak in the region of 80 S remained which vanished only under conditions destroying ribosomal material altogether. (5) Proteins were isolated from ribosomal subunits and from undissociated ribosomes and were characterised by two-dimensional gel electrophoresis techniques. Patterns of 51 spots were regularly obtained from large subunits and patterns of 41 spots from small subunits. The undissociated ribosomes showed 83 spots, most of which could be attributed to the large or the small subunit. The ribosomal proteins have molecular masses of between 11000 and 56000 Da, while the molecular mass of the total protein content of Brachionus ribosomes was estimated to be 1.8 ±0.5) ×10⁶ Da.