[Metabolism of mRNAs of membrane-bound and free-polyribosomes from rat liver cells during translation and its inhibition].

Metabolism of membrane-bound and free polyribosomal RNAs was studied under conditions of suppressed synthesis of rRNA induced by small doses of actinomycin D. Besides actinomycin D, cycloheximide was used to suppress the protein synthesis. It was demonstrated that administration of cycloheximide and actinomycin D to rats resulted in a stabilization of membrane-bound polysomal mRNA in liver cells. Simultaneously with the action of those antibiotics, free polysomal mRNA was shown to degrade in exactly the same way as in the liver of control animals. Study of poly-A-containing mRNA metabolism showed that during the first hour following rat labelling specific radioactivity of membrane-bound polysomal mRNA was higher than that free polysomal mRNA. Within the interval of 1-5 hours after labelling specific activity of mRNAs of both polysomal fractions reached the same level. In the cell-free system of protein synthesis the membrane-bound polysomes of rat liver cells appeared to be much more active as compared to the free ones. The addition of poly-U matrix to the cell-free system of protein synthesis significantly stimulated the free polysomes activity during 14C-phenylalanine incorporation into polypeptides. Interrelationship of mRNAs of membrane-bound and free polysomes in eucaryotic cells is discussed.