RIBOSOMAL PROTEINS OF ESCHERICHIA COLI .2. CHEMICAL AND PHYSICAL CHARACTERIZATION OF 30S RIBOSOMAL PROTEINS

Amino acid and tryptic peptide analyses were performed on each of the 21 30S ribosomal proteins, whose purification is described in the previous paper; 18 of the proteins are chemically unrelated by these criteria. Two proteins are very similar. One other has not been sufficiently well defined to eliminate the possibility that it is a fragment of another purified protein. In addition, there may be one protein in the 30S particle that we have not purified. We conclude that there are between 19 and 22 proteins in the 30S ribosomal subunit of Escherichia coli. The 30S ribosomal subunits used as the starting material in this work contain between 230,000 and 280,000 daltons of protein. The sum of the molecular weights of the 19 proteins, measured by high-speed equilibrium centrifugation, is 410,000 daltons. Therefore one copy of each protein cannot be accommodated by a single 30S particle. We tentatively conclude that the 30S particles of E. coli are heterogeneous. © 1969, American Chemical Society. All rights reserved.