Role of Ribosomal Protein S1 in Protein Synthesis: Effects of Its Addition to Bacillus stearothermophilus Cell‐Free System

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Abstract
Products of the f2 phage RNA‐directed protein synthesizing systems in vitro, derived from Escherichia coli and Bacillus stearothermophilus, were analyzed. In contrast to other reports, it was found that B. stearothermophilus ribosomes synthesized phage coat protein when the high‐speed (100000 x g) supernatant (S100) and ribosomal wash (crude initiation factors) of homologous origin were used. Furthermore, a marked stimulation of coat protein synthesis was observed with B. stearothermophilus ribosomes when either S100 or ribosomal wash or both from E. coli cells were used instead of the respective homologous components. The principle responsible for this stimulation was identified as the 30‐S ribosomal protein S1 present in S100 and ribosomal wash. Purified S1 from E. coli at roughly one‐to‐one molar ratio to ribosomes resulted in about 10‐fold stimulation of the incorporation of [14C]valine when added to the B. stearothermophilus system. This stimulation was observed mainly in the synthesis of coat protein and replicase.