Current views on chloroplast protein import and hypotheses on the origin of the transport mechanism.
Most chloroplastic proteins are synthesized as precursors in the cytosol prior to their transport into chloroplasts. These precursors are generally synthesized in a form that is larger than the mature form found inside chloroplasts. The extra amino acids, called transit peptides, are present at the amino terminus. The transit peptide is necessary and sufficient to recognize the chloroplast and induce movement of the attached protein across the envelope membranes. In this review, we discuss the primary and secondary structure of transit peptides, describe what is known about the import process, and present some hypotheses on the evolutionary origin of the import mechanism.
Archer
E K
EK
Department of Biology, Trinity College, Hartford, Connecticut 06106.
Keegstra
K
K
D000595:Amino Acid Sequence; D005075:Biological Evolution; D001692:Biological Transport; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism*; D008954:Models, Biological; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism*; D011487:Protein Conformation; D011498:Protein Precursors / Q000378:metabolism*; D021382:Protein Sorting Signals / Q000737:chemistry / Q000378:metabolism*
D002352:Carrier Proteins; D010455:Peptides; D010940:Plant Proteins; D011498:Protein Precursors; D021382:Protein Sorting Signals