Ribosomal protein S3 is one of the proteins from the small ribosomal subunit. In Escherichia coli, S3 is known to be involved in the binding of initiator Met-tRNA. It belongs to a family of ribosomal proteins which, on the basis of sequence similarities [1], groups:

• Eubacterial S3.
• Algal and plant chloroplast S3.
• Cyanelle S3.
• Archaebacterial S3.
• Plant mitochondrial S3.
• Vertebrate S3.
• Insect S3.
• Caenorhabditis elegans S3 (C23G10.3).
• Yeast S3 (Rp13).

S3 is a protein of 209 to 559 amino-acid residues. As signature patterns, we selected a conserved region located in the C-terminal section.