Cerebral Protein Synthesis II. INSTABILITY OF CEREBRAL MESSENGER RIBONUCLEIC ACID-RIBOSOME COMPLEXES

Abstract Ribosomal preparations isolated from rat cerebral cortex exhibited basal amino acid-incorporating activities comparable to those observed with the analogous preparations from rat liver. In each instance, polyribosomes larger than the tetramer were most active in protein synthesis in vivo and in vitro. However, following the initial incorporation of radioactive amino acids into heavy polyribosomes, a substantial portion of the radioactivity incorporated became associated with the lighter ribosomal species in the cerebral but not in the hepatic systems. Cerebral ribosomal preparations contained a smaller proportion of heavy polyribosomes than the corresponding hepatic ribosomes. These cerebral polyribosomes dissociated more rapidly than hepatic polyribosomes during incubation in amino acid-incorporating systems. Under these conditions, disruption of cerebral polyribosomes was accompanied by greatly accentuated incorporation of phenylalanine in response to polyuridylic acid. Nevertheless, the cerebral systems uniformly contained significantly lower ribonuclease activities than the corresponding hepatic preparations. Moreover, cerebral polyribosomes exhibited greater sensitivity to disruption than hepatic polyribosomes in the presence of low concentrations of pancreatic ribonuclease or Mg2+. The data support the concept that certain cerebral messenger RNA-ribosome complexes are unusually labile. The possible relationship of these findings to the specialized biological functions of the central nervous system is discussed.