S5
S5 has two definite domains of alpha helices and beta-pleated sheets. Its molecular mass is 17500. There are two distinct sections of S5 that may be interaction sites for 16S rRNA. This was found by mapping various mutations that occurred in S5 to these distinct sections of the protein. The mutations in the S5 protein cause several different phenotypes to occur. These include ribosome ambiguity or ram, reversion from streptomycin dependence and resistance to spectinomycin. The mutations suggest that protein S5 is involved in translocation and translational fidelity (Ramakrishnan and White 1992).

S6
The crystal structure of protein S6 shows that the S6 protein consists of only 101 amino acid residues. It is composed of one “four-stranded anti-parallel beta-sheet with two alpha helices packed on one side,” (Lindahl et al 1994). RNA interacts with the edge of the beta sheet (Wimberly 2000).

S9
Protein S9 has one main globular domain, and one long extension, either one the carboy- end or the amino-end, which protrudes away from the rest of the protein like a long tail. The extension is believed to be used to interact and make contact with 16S rRNA. The extension is narrow which allows for the close contact with the rRNA. Also, along the extension are basic amino acid residues, which neutralize the rRNA backbone’s charge repulsion (Wimberly et al 2000).

S12
S12 consists of globular domains, and an extended carboxyl or amino end tail. This allows the protein to make contact with 16S RNA. The globular domain is located on the interface side of the 16S rRNA. The tail weaves through the body of 16S rRNA and then folds into a small alpha helix. The alpha helix can then interact and make contact with proteins S8 and S17 (Wimberly et al 2000).