Protein import into chloroplasts

Three proteins from the chloroplastic outer envelope membrane and four prot eins from the inner envelope membrane have been identified as components of the chloroplastic protein import apparatus. Multiple molecular chaperones and a stromal processing peptidase are also important components of the imp ort machinery. The interactions of these proteins with each other and with the precursors destined for transport into chloroplasts are gradually being described using both biochemical and genetic strategies. Homologs of some transport components have been identified in cyanobacteria suggesting that at least some of import machinery was inherited from the cyanobacterial anc estors that gave rise to chloroplasts.