IDENTIFICATION AND LOCALIZATION OF RAB6, SEPARATION OF RAB6 FROM ERD2AND IMPLICATIONS FOR AN UNSTACKED GOLGI, IN PLASMODIUM-FALCIPARUM

The rab6 gene product in mammalian cells and yeast is localized to and regulates protein transport in the medial and ti ans Golgi cisternae, as well as the trans Golgi network. We have identified a homologue in the malaria parasite Plasmodium falciparum which displays a rab-like sequence that is 62.4% identical to mammalian rab6. In addition the pa rasite gene (Pfrab6 gene) contains an N-terminal hydrophobic domain, u nique to P. falciparum. Antibodies developed to Pfrab6 localize protei n in 4-7 well-resolved sites in a ring-stage parasite. as detected by high resolution fluorescence microscopy. This suggests that there are multiple, distinct foci of medial/trans Golgi membranes in a ring. ERD 2 is a cis Golgi marker in mammalian cells. The plasmodial homologue o f ERD2 (PfERD2) is concentrated in a single perinuclear region in a ri ng-stage parasite. This site is distinct from the Pfrab6 membranes, in dicating that early and late Golgi markers can be segregated in P. fal ciparum. Mammalian cells contain a single Golgi complex where cis medi al and trans markers are tightly stacked in closely apposed cisternae. In P. falciparum-rings however, rab6-associated membranes are not inv ariably 'stacked' with an ERD2 structure. In immunoelectron microscopy studies, both the PfERD2- and Pfrab6-associated membranes appear tubu lovesicular in nature, devoid of cisternal morphology. Hence the Golgi of ring stage parasites may comprise of multiple, 'unstacked' tubulov esicular clusters,suggesting a primitive organization of the organelle is Plasmodia. Copyright (C) 1996 Elsevier Science B.V.