Three-dimensional organization of the 30S ribosomal proteins from Escherichia coli. I. Preliminary classification of the proteins.

30S ribosomal subunits from Escherichia coli were reacted with three protein reagents. After reaction, the ribosomal proteins were extracted and examined; of the 20 proteins known to compose the particle, nine did not react with any of the three reagents. We have tentatively classified these proteins as "internal," and the remaining eleven as "external." A strong correlation was found between these results and the sequence of assembly. Those proteins which enter the assembly process early are classed as internal, whereas those proteins found to participate later in the assembly sequence are classed as external.