Figure 1: A schematic drawing shows the signal sequence of a protein and how it is cleaved by the signal peptidase. An amino acid in the signal part is depicted as a white circle with a black number to indicate its sequential position, while in the mature protein depicted as a black circle with a white number. The signal sequence contains Ls residues and the mature protein Lm residues. The cleavage site is at the position (−1, ), that is, between the last residue of the signal peptide sequence and the first residue of the mature protein.