Protein Translocation at the Envelope and Thylakoid Membranes of Chloroplasts

Endosymbiotic evolution has resulted in the transfer of genes encoding the vast majority of the protein components of plastids to the nuclear genome. In response to this displacement of genetic material, plastids have evolved a system to post-translationally import nuclear encoded preproteins from their site of synthesis on cytoplasmic ribosomes. The protein import process can be viewed as a cascade of protein targeting events that are governed by a hierarchy of topogenic sequences. The targeting sequences are sequentially decoded resulting in the localization of the polypeptide to the appropriate organellar subcompartment (for review see Refs.