Relationship between Protein Synthesis and RNA Content in Skeletal Muscle

Abstract

EXTENDING our studies on the adaptation of muscle synthesis to dietary stress^1,2, we investigate here the relationship between concentrations of tissue RNA and rates of protein synthesis. Dietary regimes which depress protein synthesis also lead to a fall in tissue RNA content^3,4. This fall may reflect a reduced need for cellular RNA components, or it may itself be of primary importance in determining the rate of protein synthesis. More than 80% of muscle RNA is ribosomal and this proportion appears to be maintained during protein depletion⁵, so that a change in RNA also reflects a change in ribosome content. If alteration in ribosomal content effects control, then this alteration may be termed a change in the ribosomal capacity for protein synthesis. If, however, a change in synthesis is brought about by alterations in the other factors modulating each phase of translation, then it is a change in the ribosomal efficiency. This will be demonstrable as alterations in the amount of protein synthesized per unit RNA. We have investigated the extent to which alterations in rates of protein synthesis result from changes in the capacity for and the efficiency of protein synthesis in muscle.