Purification of myosin mRNP translational control RNA and its inhibition of myosin and globin messenger translation

Since oligo(U)-containing tcRNA was first found in embryonic muscle [ 1 ] it has also been observed in Artemia salina [2] and connective tissue [3]. In all cases this tcRNA has been shown to inhibit protein synthesis. Only in the studies from muscle cells has this inhibition been shown to have a high degree of discrimination between messengers. In this case, highly purified oligo(U)-containing tcRNA was shown to interact stoichiometrically with myosin mRNA and inhibit its translation while having little effect on the translation of other messengers [4]. The ollgo(U)containing tcRNA, isolated from Artemia salina [2] may, inhibit protein synthesis in a non-selective manner by acting directly on the ribosomes [2]. Oligo(U)-containing tcRNA, isolated from connective tissue, inhibits both globin and collagen mRNA translation [3] ; however, the inhibition of collagen synthesis is significantly greater than that of globin. Our studies have suggested that the sequence of addition of the reactants to the protein synthesizing system is important in determining the mode of action of this tcRNA [4,5]. We have further examined this in an attempt to correlate these apparently conflicting reports concerning the inhibitory effect of oligo(U)containing tcRNA. In this report we verify that myosin oligo(U)-containing tcRNA is associated with myosin mRNF% and not with ribosomes co-sedimenting with the mRNPs. In addition, we find that it is necessary both to use stoichiometric amounts of mRNA and tcRNA and to add tcRNA and mRNA in the proper sequence to the reaction mixture in order to observe a selective inhibition of messenger trans-