Amino-Terminal Sequences of Some Escherichia coli 30S Ribosomal Proteins and Functionally Corresponding Bacillus stearothermophilus Ribosomal Proteins1

Ken-Ichi Higo, Kenneth Loertscher
1974 Journal of Bacteriology  
Amino-terminal sequences of five purified Escherichia coli 30S ribosomal proteins (S4, S9, S10, S16, and S20) were compared with those of their functionally corresponding Bacillus stearothermophilus ribosomal proteins identified previously by the reconstitution technique. An automatic Edman degradation method was used for sequence determinations. The sequence of the first 30 residues is presented, except that only the first 25 residues are shown for the S20 pair. Substantial (40 to 70%)
more » ... (40 to 70%) sequence homologies have been observed in every case. The results show that the pairs of functionally equivalent proteins, previously identified by the reconstitution technique, are also chemically related. Thus, the present chemical studies give further support for the previous conclusion that two ribosomes with different properties, 30S subunits from E. coli and B. stearothermophilus, have the same fundamental structural organization. Earlier experiments from this laboratory demonstrated that functionally active 30S ribosomal subunits can be reconstituted from the 16S ribosomal ribonucleic acid (rRNA) of one species of bacteria and that the ribosomal proteins (r-proteins) can be reconstituted from a distantly related species (18). It has been suggested that the specific part of r-proteins interacting with the rRNA may have a structural feature in common with "corresponding proteins" from different bacterial species. In extending this work further, we have recently performed experiments to determine whether r-proteins from distantly'related bacterial species can be shown to be functionally equivalent on a one-to-one basis (11). For this purpose, we fractionated 30S r-proteins from Bacillus stearothermophilus (B proteins) and looked for functional correspondence between these proteins and Escherichia coli 30S r-proteins (E proteins) by using the reconstitution technique. The properties of the ribosomes from these two organisms are different in several respects, as discussed in previous papers (11, 18) . There are distinct chemical differences between the 16S RNAs of the two species (18, 21 and papers cited therein). Moreover, the proteins from 30S subunits differ with respect to their column chro-I Paper no. 1707 of the Laboratory of Genetics, University of Wisconsin, Madison, Wis. 53706. matographic (11) or gel electrophoretic patterns (1, 18, 26) , their ability to confer heat resistance upon the ribosomal subunits (9, 18, 20) , and their immunochemical properties (29). In addition, it is known that B. stearothermophilus 30S subunits cannot translate the coat protein and the replicase cistrons of RNA messenger from f2 and related RNA phages, whereas E. coli 30S subunits can (15). However, we have found that most, if not all, of the E proteins have functionally equivalent counterparts among B proteins, supporting the conclusion that the fundamental structural organization of ribosomes is the same throughout prokaryotic organisms (11). Complete interchangeability between E proteins and B proteins in the 30S reconstitution was somewhat surprising in view of the known differences between the ribosomal proteins of the two species described above, and especially surprising in view of the results of the immunochemical studies which showed very weak crossreaction between E and B ribosomal proteins (29). In addition, our previous conclusion on the conservation of ribosome structure, as well as r-proteins, depended for the most part on the functional assay of proteins by the reconstitution technique (11). Since we cannot completely exclude fortuitous stimulation of activity of protein-deficient reconstituted "30S" particles by some unrelated proteins, rigorous proof of 180 on May 7, 2020 by guest
doi:10.1128/jb.118.1.180-186.1974 fatcat:fifkx4abibby3ir3me5a7guapu