The cytoplasmic translational inhibitory RNA of chick embryonic muscle: cloning and sequence of a subspecies which is antisense RNA.

A cytoplasmic translation inhibitory ribonucleoprotein (iRNP), about 10-12S in size and containing a heterogeneous class of RNA (iRNA) in the 60-140 nucleotide size range, has been previously isolated from 13-14 day old chick embryonic leg and breast muscle. Both iRNA and iRNA are potent inhibitors of mRNA translation in vitro. A cDNA library for iRNA was prepared in pUC18 vector. The 114 nucleotide insert of one clone was subcloned in pBluescript vector. The in vitro transcript of this insert (only the 5'-3' orientation and not the reverse orientation) showed inhibition of muscle poly(A)+ mRNA translation in vitro. The derived sequence of the iRNA indicates that it is a new sequence in which 27 nucleotides at the 3' and 5' ends can form base paired stem. Hybridization experiments and sequence analysis indicate that this iRNA has complementary (antisense) sequence to a highly conserved domain of the 28S eukaryotic rRNA and to a 5' leader segment of a muscle mRNA. These results suggest that iRNA mediated translational inhibition may act as a novel mechanism of controlling cellular mRNA levels in embryonic muscle and thus, acts in conjunction with the transcriptional control of myogenesis.