Lack of ribosomal protein S1 in Bacillus stearothermophilus

The 30S ribosomal subunit of Bacillus stearothermophilus migrated as a single band when electrophoresed on agarose-acrylamide composite gels. The addition of the ribosomal protein S1 purified from Escherichia coli resulted in the appearance of an additional band migrating more slowly; 14C-labeled S1 of E. coli was shown to be associated only with this form. Antibody against E. coli protein S1 did not crossreact with either the total 30S ribosomal proteins or the postribosomal supernatant from B. stearothermophilus. These results indicate that B. stearothermophilus lacks a protein equivalent to E. coli S1 and may explain our previous finding [Eur. J. Biochem. 56, 15-22 (1975) that E. coli S1 greatly stimulated the translation by B. stearothermophilus ribosomes of f2 phage RNA.