A common feature in cells of all living organisms is the export of proteins from their site of synthesis, usually the cytoplasm, to other destinations either inside or outside the cell. To
achieve this, transported proteins are generally synthesized as a precursor with an aminoterminal signal peptide, which is recognized and exported by cellular sorting and translocation machineries. Although the primary structure of signal peptides is poorly conserved, usually three functional domains are present: first, a positively-charged amino terminus (N-region); second, a central hydrophobic domain (H-region); and third, a polar caroxyl-termindaol main (C-region), specifying the signal peptidase (S Pase) cleavage site.
Zie: Summary and general conclusions.