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Polyribosomes in Rat Tissues

III. The Response of the Polyribosome Pattern of Rat Liver to Physiologic Stress¹

McArdle Laboratory for Cancer Research, The Medical School, University of Wisconsin, Madison, Wisconsin

The size distribution of polyribosomes prepared from the postmitochondrial supernatant of rat liver is modified by prolonged fasting, partial hepatectomy, and the administration of dinitrophenol or carbon tetrachloride. The carbon tetrachloride also causes the release of ribosomes bound to the endoplasmic reticulum, in addition to the extensive breakdown of the polyribosomes. The results suggest that the size distribution is not simply a function of the relative concentrations of the ribosomes and mRNA,³ but rather depends on the energy supply and the relative sizes of the mRNA that is being produced. In general, the proportion of ribosomes sedimenting in the heavy polyribosome region appears to correlate with the predicted growth rate (protein synthesizing capacity) of the tissue.

¹ This work was supported in part by a departmental grant, No. CA-07125, and a training grant, No. CRTY-5002, from the National Cancer Institute.

³ The abbreviations used are: mRNA, messenger ribonucleic acid; DNP, dinitrophenol; S₂ postmitochondrial supernatant; DOC, deoxycholate; TKM buffer, 0.05 M tris(hydroxymethy) aminomethane, 0.025 M KCl, and 0.005 M MgCl₂, pH 7.5; and ATP, adenosine triphosphate.

² Present address: Department of Biochemistry, Medical School, University of Manitoba, Winnipeg, Manitoba, Canada.

Received 5/ 7/65. Revised 8/13/65.