Physiology of rat-liver polysomes. Protein synthesis by stable polysomes

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Abstract
Certain qualitative aspects of protein synthesis in the livers of starved, starved-re-fed and actinomycin D-treated rats have been examined by poly-acrylamide-gel electrophoresis. Animals were exposed to a mixture of C14-labelled acids for 18-20 min. and killed, and an ultrasonic extract of newly formed protein in microsomal vesicles was prepared and examined by gel electrophoresis. In normal and starved-re-fed animals, 27% of the newly synthesized protein was albumin. During starvation, when RNA synthesis was decreased, the percentage of newly formed protein as albumin rose. After actinomycin D treatment of starved-re-fed rats, when only stable messenger RNA persisted in the cytoplasm, albumin synthesis increased to 63% of the total. This finding suggested that albumin was the primary protein synthesized on stable messenger RNA.