 For example, one well-known example is the dileucine motif, in which a leucine amino acid (aa) residue is followed immediately by another leucine or isoleucine residue.An even simpler example is the tyrosine based signal, which is YxxØ (a tyrosine residue separated by 2 aa residues from another bulky, hydrophobic aa residue).The accompanying figure shows how a small part of a protein can interact specifically with another protein, so these short signalling motifs should not be surprising.