Ribosomal protein S12 is one of the proteins from the small ribosomal subunit. In Escherichia coli, S12 is known to be involved in the translation initiation step. It is a very basic protein of 120 to 150 amino-acid residues. S12 belongs to a family of ribosomal proteins which, on the basis of sequence similarities [1], groups:

• Eubacterial S12.
• Archaebacterial S12.
• Algal and plant chloroplast S12.
• Cyanelle S12.
• Protozoa and plant mitochondrial S12.
• Yeast S28.
• Drosophila mitochondrial protein tko (Technical KnockOut).
• Mammalian S23.

As a signature pattern, we selected the best conserved regions in these proteins, located in the center of each sequence.