Assembly Mapping of 30 S Ribosomal Proteins from Escherichia coli

Further studies were performed on the sequence of addition of proteins to 16 S RNA during the in vitro reconstitution of 30 S ribosomal subunits from Escherichia coli. Direct binding of protein S17 to 16 S RNA was studied in detail, and the following results were obtained: (a) under reconstitution conditions, a maximum of approximately 1 mole of S17 is bound per mole of 16 S RNA, either alone, or in the presence of all other 30 S proteins; (b) S17 binds only to 16 S RNA and not to 23 S RNA; and (c) radioactive S17–16 S RNA complexes are directly converted (without dissociation) to 30 S subunits by the addition of excess unlabeled total 30 S proteins. From these results, we conclude that the binding of S17 to 16 S RNA is specific. We have also determined the positions of S15, S16, S17, and S12 in the assembly map and have clarified subsequent interactions depending on these proteins. A revised assembly map is presented which incorporates the additional information obtained from these experimental results.