Labelling kinetics of ribosomal RNA's in rat brain

Slices of cerebral cortex and cerebellum from two-week-old rats were incubated in the presence of [14C] uridine and [methyl-3H] methionine. Incorporation of 14C- and 3H-radioactivity into 18S and 28S RNA's of the two tissues was analysed by sucrose-density-gradient centrifugation. The results show that the rates of synthesis of ribosomal RNA's as well as the pattern of methylation in the two tissues were different. Some of these differences may be ascribed to factors such as pool sizes, intracellular rate of transport of the precursors by other pathways, etc. Examination of the results indicates that some differences may consist in the actual biosynthesis and maturation of ribosomal RNA's.