Requirement of a large amount of polyuridylate for efficient polyphenylalanine synthesis by staphylococcal ribosomes.

Polyuridylic-acid-directed polyphenylalanine [poly (U)-directed poly (Phe)] synthesis by Staphylococcus aureus ribosomes (washed in 1.0 M NH4Cl) increased linearly with increasing amount of poly (U) : the synthesis by washed staphylococcal ribosomes in the presence of about 800μg poly (U)/ml reached the same level as that by ribosomes of Escherichia coli Q13 at the optimum poly (U) concentration (about 40μg/ml). Binding of either 70S ribosomes or 30S ribosomal subunits of S. aureus U9 to poly (U) was less than that of E. coli Q13. Sedimentation analysis in a sucrose gradient showed that the amount of the heavy complex produced by interaction of poly (U) and ribosomes of S. aureus U9 was small at a high poly (U) concentration (1750 μg/ml), whereas that of E. coli Q13 was large even at 500 μg poly (U)/ml. These results suggest that low ability of the washed S. aureus ribosomes to synthesize poly (Phe) chiefly results from poor affinity of ribosomes for poly (U), since no ribonuclease activity could be found in the washed ribosomes.