Involvement of Aminoacyl-tRNA Transfer Factors in Polyphenylalanine Synthesis by Rice Embryo Ribosomes

Two distinct heat labile factors (I and II) were found to be required for the in vitro synthesis of polyphenylalanine by rice ribosomes (Oryza sativa var. Bluebonnct) and polyuridylic acid. These factors were present in both the crude supernatant and on crude ribosomes. Factor I was removed from the crude ribosomes by [ill] (0.6%), while factor II was eliminated from deoxycholate washed ribosomes by a 0.5 m KCl wash.Factor I was purified from crude supernatant by calcium phosphate absorption and elution followed by polyacrylamide gel electrophoresis. Purified factor I was able to substitute for crude supernatant in supporting polyphenylalanine synthesis with deoxycholate washed ribosomes.The supernatant fraction from a KCl wash of deoxycholate ribosomes was found to contain factor II but no factor I activity. Factor II activity was also present in the calcium elutant fraction prepared from crude supernatant. Both factors I and II were required in order to substitute for crude supernatant in supporting polyphenylalanine synthesis with KCl washed ribosomes.The optimum Mg concentration for polyphenylalanine synthesis with d-oxycholate ribosomes was 4.5 mm with crude supernatant, and 6.5 mm with purified factor I. However, with KCl ribosomes supplemented with factors I and II, the optimum was 8.5 mm.Analytical ultracentrifugation Schlieren patterns indicated that KCl washed ribosomes contained a significant quantity of ribosomal subunits.