Inhibition by soluble ribonucleic acid of stimulatory effect of liver template ribonucleic acid.

1. Liver soluble RNA (s-RNA) and, to a smaller extent, Escherichia coli s-RNA inhibited the stimulation of [(14)C]leucine incorporation into protein in an E. coli S-30 system brought about by liver microsomal RNA or polyuridylic acid as template. 2. The inhibitory activity was associated with the fraction of the s-RNA possessing transfer-RNA activity. 3. The inhibition was exercised at a stage after charging of the s-RNA with amino acid. 4. Neither the method of preparation of the s-RNA nor its state of amino acid acylation affected its inhibitory action. 5. Stimulation of [(14)C]phenylalanine incorporation by polyuridylic acid or by liver microsomal RNA was not inhibited by addition of s-RNA. 6. It appears that excess of s-RNA inhibits the ambiguous incorporation of leucine with polyuridylic acid and also that something similar occurs with a natural template. 7. Estimation of messenger activity of samples of RNA should be carried out only after removal of s-RNA.