Breakdown of ribosomal RNA in rabbit reticulocytes

To study the breakdown of the RNA of ribosomes, reticulocytes from anemic rabbits were incubated in a synthetic culture medium for several hours. Ribosomal RNA was isolated from ribosomal subunits by phenol/chloroform extraction and analyzed on nondenaturing and denaturing sucrose gradients. For comparison RNA from erythroid bone marrow cells and non-incubated reticulocytes were used. The sedimentation analysis of the 28 S rRNA suggests that the breakdown during maturation of reticulocytes involves the occurrence of characteristic intermediate products, sedimenting with coefficients of about 21 S and 18 S. In contract to the breakdown of 28 S rRNA there were no apparent distinct cleavage products of 18 S RNA. The results suggest a preferential cleavage of the 28 S rRNA at specific sites, possibly owing to a particular exposure of the RNA. The breakdown of 18 S rRNA seems to occur in a random manner.