title: Protein import into the photosynthetic organelles ofPaulinella chromatophoraand its implications for primary plastid endosymbiosis.
abstract: The rhizarian amoebaPaulinella chromatophoraharbors two photosynthetically active organelles of cyanobacterial origin that have been acquired independently of classic primary plastids. Because their acquisition did take place relatively recently, they are expected to provide new insight into the ancient cyanobacterial primary endosymbiosis. During the process ofPaulinellaendosymbiont-to-organelle transformation, more than 30 genes have been transferred from the organelle to the host nuclear genome via endosymbiotic gene transfer (EGT). The article discusses step-by-step protein import of EGT-derived proteins intoPaulinellaphotosynthetic organelles with the emphasis on the nature of their targeting signals and the final passage of proteins through the inner organelle membrane. The latter most probably involves a simplified Tic translocon composed of Tic21- and Tic32-like proteins as well as a Hsp70-based motor responsible for pulling of imported proteins into the organelle matrix. Our results indicate that although protein translocation across the inner membrane ofPaulinellaphotosynthetic organelles seems to resemble the one in classic primary plastids, the transport through the outer membrane does not. The differences could result from distinct integration pathways ofPaulinellaphotosynthetic organelles and primary plastids with their respective host cells.
authors.affiliation: Department of Genomics, Faculty of Biotechnology, University of Wrocław, ul. Przybyszewskiego 63/77, 51-148 Wrocław, Poland.
authors.forename: Paweł
authors.initials: P
authors.lastname: Mackiewicz
authors.forename: Andrzej
authors.initials: A
authors.lastname: Bodył
authors.forename: Przemysław
authors.initials: P
authors.lastname: Gagat
keywords: Endosymbiosis; Molecular motor; Plastid; Protein import; Signal peptide; Vesicular trafficking