Fate of a Synthetic Polynucleotide Directing Cell-Free Protein Synthesis II. Association with Ribosomes

Tritiated-poly U, when added to cell-free extracts of Escherichia coli, became associated with ribosomes. This association occurred at 3 degrees C and did not require high-energy phosphate compounds. Small amounts of tritiated polyuridylic acid produced polydisperse ribosomal aggregates with sedimentation constants of approximately 100 to 130. C(14)-phenylalanine initially was incorporated into protein only on these particles, which suggests that they are the sites of polyphenylalanine synthesis.