Basic aspects of protein synthesis in muscle.

Abstract

The embryonic muscle serves as an excellent tissue for the study of synthesis of specific proteins in cell-free systems. We have used homologous and heterologous cell-free systems to demonstrate specific messenger RNAs present in several size classes of muscle polysomes. These cell free systems, in which the added specific mRNAs were forced to compete with endogenous mRNAs, demonstrated a requirement for initiation factors washed from ribosomes of tissues normally synthesizing the protein in question. This held true between red and white muscle initiation factors in the ability to recognize added mRNA coding for myoglobin, even though initiation factors from either muscle source, but not from a non-muscle source, were effective in the synthesis of myosin on heterologous ribosomes. The component of the initiation factors which appears to be specific has occurred in the IF3 fraction from DEAE cellulose chromatography. This IF3 preparation has been separated on phosphocellulose columns into components demonstrating specificity towards different mRNA species, as demonstrated both by binding of labelled mRNAs to ribosomes and also by their effectiveness in the synthesis of the respective proteins in heterologous cell free systems. The possibility of post-transcriptional control of specific protein synthesis suggested by this work could provide a means of controlling and coordinating synthesis of groups of special proteins during differentiation or more stable cell states.