Ribosomal protein S5 is one of the proteins from the small ribosomal subunit. In Escherichia coli, S5 is known to be important in the assembly and function of the 30S ribosomal subunit. Mutations in S5 have been shown to increase translational error frequencies.

The crystal structure of the S5 protein has been solved [1] and consists of two separated domains (see <PDB:1PKP>). An N-terminal domain which displays some structurale homology to the dsRBD domain (α-β(3)-α) (see <PDOC50137>) and a mainly helical C-terminal domain that interacts with S8. The dsRBD domain of the S5 protein interacts with the 16S RNA [2].

S5 belongs to a family of ribosomal proteins which, on the basis of sequence similarities [3,4], groups:

• Eubacterial S5.
• Cyanelle S5.
• Red algal chloroplast S5.
• Archaebacterial S5.
• Mammalian S2 (LLrep3).
• Caenorhabditis elegans S2 (C49H3.11).
• Drosophila S2.
• Plant S2.
• Yeast S4 (SUP44).
• Fungi mitochondrial S5.

S5 is a protein of 166 to 254 amino-acid residues. The signature pattern for this protein is based on a conserved region, rich in glycine residues located in the N-terminal domain. The profile we developed covers the entire N-terminal dsRBD domain.