Cleavage-Site Motifs in Protein Targeting Sequences

All living cells have at least a rudimentary ability to route proteins to different subcellular compartments: Gram-positive bacteria can distinguish between the cytoplasm, the plasma membrane, and the external medium; Gram-negative bacteria can in addition put proteins into the periplasmic space or the outer membrane; and eukaryotic cells with their multitude of subcellular organelles have evolved a highly complex system for intracellular protein transport (1–3).