DETACHMENT OF RIBOSOMES FROM DOG PANCREAS POLYSOMES WITHOUT CONCURRENT POLYPEPTIDE SYNTHESIS

1. Ribonucleoprotein particles were isolated from dog pancreas cytoplasm and shown to contain polysomes by zone sedimentation velocity analysis, sensitivity to ribonuclease, amino acid incorporation and electron microscopy. The parameters of amino acid incorporation into protein were determined, using as precursor either aminoacyl-tRNA or an amino acid mixture. 2. It was found that release of monomeric ribosomes from polysomes during incorporation from free amino acids was independent of polypeptide synthesis. Ribonuclease activity does not appear to be responsible for this effect. This breakdown of polysomes during incubation in the incorporation mixture was dependent on the presence of GTP and ATP. Polysomes were stabilized under these conditions by NH4+, K+, Mg2+, or by aminoacyl-tRNA. Since the components responsible for the breakdown phenomena were those participating in the known reactions of protein synthesis, the release of ribosomes may result from the malfunction of the mechanism that links movement of mRNA through the ribosomal decoding site to amino acid incorporation into polypeptides. © 1969.