Spermidine requirement for Bacillus thuringiensis ribosomes in cell-free phenylalanine incorporation

A cell-free system from Bacillus thuringiensis was found to actively incorporate phenylalanine into hot trichloroacetic acid-precipitable material in the presence of synthetic polynucleotide, ribosomes, S-100 supernatant, an energy-generating system, and guanosine triphosphate. Phenylalanine incorporation was absolutely dependent on the presence of spermidine in addition to magnesium ions, even when highly purified ribosomes were used. The spermidine effect could not be attributed to inhibition of nucleases. The ribosomal and supernatant fractions from Escherichia coli and B. thuringiensis could be substituted for each other in this system. The spermidine requirement was shown to be limited to the B. thuringiensis ribosome fraction.