Ribosome Turnover Research Articles

Turnover of liver ribosomes in ethanol-intoxicated rats

Turnover of liver ribosomes in ethanol-intoxicated rats

The ribosomes of pear fruit. Their synthesis during the climacteric and the age-related compensatory response to ionizing radiation.

Maceration at liquid nitrogen temperatures, use of poly-vinylpyrrolidone, and careful pH control are essential to the isolation of ribosomes and polysomes from deciduous fruit tissue. Characteristics of the ribosomes and constituent RNA are described. The distribution of ribosomes among monomer and polymer forms remains relatively constant until fruit reach the climacteric peak, after which there is a notable decline in the polymeric forms. In contrast to the relative stability in size distribution there is a marked change in ribosomal turnover during the climacteric rise. A transitory increase in rate of ribosomal synthesis is followed by a rapid decline coincident with the final portion of the climacteric rise. No incorporation of radioactive base into ribosomes could be detected once fruit had reached the climacteric peak.Coincidence of radioactivity with the ribosomal RNA on methylated albumin-Kieselguhr chromatograms and complete inhibition of ribosomal RNA synthesis by actinomycin D confirm that radioactive nucleotide was incorporated into newly synthesized ribosomes. Data are presented to distinguish between a cellular response to injury, as may result from the preparation of tissue slices, and the effects of physiological age. Superimposed intracellular radiation injury stimulates the synthesis of new ribosomes and underscores a major transition in the dynamics of the ribosomal system coincident with the climacteric rise.

Interferon action in heterokaryons.

SummaryChick interferon was active in chick red blood cell-human fibroblast heterokaryons, whereas it was inactive in the human fibroblasts without fused chick nuclei. The heterokaryons were much less sensitive to human interferon than were the human fibroblasts without chick nuclei. Both human and chick interferons together were more active in heterokaryons than was either interferon alone. Ribosomal turnover studies in heterokaryons and in the human cells without chick nuclei suggest the possibility that the site of interferon action may not be on the ribosomes.

Turnover of Liver Ribosomes in Fed and in Fasted Rats

Abstract Evidence from many sources indicates that the ribonucleic acid and protein of normal animal tissues are replaced more rapidly than are the cells themselves. However, the significance of this macromolecular turnover and the mechanisms that regulate synthesis in concert with catabolism to maintain cellular composition have remained obscure. In beginning a study of factors that influence protein and RNA turnover in mammalian cells, we have compared the rates of synthesis and degradation of liver cytoplasmic ribosomes in fed and in fasted animals. Synthesis was measured by labeling ribosomal protein and RNA and by measuring the rate at which the specific activities decreased owing to continuing synthesis from unlabeled precursors. In fed, nearly mature animals, degradation approximates synthesis. In fasting, degradation exceeds synthesis and was measured as the difference between rates of synthesis and of net loss of liver ribosomes. Our results indicate that ribosomal protein and RNA are replaced at the same rate. The normal kinetics are first order, with turnover half-times of 5 days. During starvation, the cellular ribosome content decreases steadily due to an increased degradative and a diminished synthetic rate.