Functional correspondence between 30S ribosomal proteins of Escherichia coli and Bacillus stearothermophilus

30S ribosomal proteins from Bacillus stearothermophilus (B. proteins) have been fractionated and characterized with respect to their ability to replace various E. coli 30S proteins (E. proteins) in the E. coli 30S ribosome reconstitution system. The functional counterparts of all the E. proteins, except S1, S6, S9, and S13, have been tested. In all cases, B. proteins can substitute for E. proteins. Several purified B. proteins are chemically different from their functionally homologous E. proteins. Five B. proteins are immunochemically related to E. proteins; this set includes two proteins that could not be tested in the reconstitution system (S9 and S13). Thus most, if not all, of the E. proteins have functionally equivalent counterparts among B. proteins, even though properties of the two ribosomes are different in several respects. These results suggest that the fundamental structural organization of ribosomes may be the same throughout prokaryotic organisms.