Polyribosomes in rat-liver preparations.

1. The distribution of rat-liver polyribosomes in sucrose density gradients has been investigated with regard to the effects of the preparative procedures and the physiological and pathological condition of the animal. 2. By using carefully defined conditions, three principal polyribosomal fractions have been isolated with S(20,w) values of 340, 275 and 225s in addition to the dimerized 120s and single 80s ribosomes. 3. The polyribosomes were very sensitive to treatment with ribonuclease and to mechanical stresses. 4. Incubation of dispersed hepatic cells and also cell-free preparations with puromycin in the presence of ATP and phosphoenolpyruvate caused rapid partial degradation of the polyribosomes. Treatment of the dispersed cells with actinomycin D also degraded the polyribosomes. 5. The liver polyribosomes of rats not raised under pathogen-free conditions and possibly of rats with an arthritic syndrome may be more fragile than those of healthy pathogen-free animals. 6. Treatment of pathogen-free rats with drugs stimulating liver anabolism profoundly affected the distribution of polyribosomes in sucrose density gradients.