Proposed scheme for the transport of parasite proteins to the erythrocyte plasma membrane. (A) Many of the individual events depicted in Figures 1 to 5 are captured in a single (∼ 70 nm) section from an IRBC treated with AlF. Coated vesicles budding from the PVM form a vesicle chain that spans the RBC cytosol and associates with one end of a Maurer cleft. A vesicle in line with the (left-hand side) of a Maurer cleft is observed at the RBC membrane (white arrow). The Maurer cleft is anchored to the RBC plasma membrane via actin. Original magnification, × 20 000. (B) Schematic representation of the transport of Pf EMP1 and Pf EMP3 (and other parasite proteins) to the RBC cytosol and plasma membrane. Steps 1 and 2 are hypothetical pathways. Pf Sec31, Pf Sar1p, and possibly Pf Sec23p (which is in the Pf genome but is uncharacterized) are exported to the RBC cytosol in which they form Pf COPII, facilitating vesicle formation at the PVM (steps 3-5). Vesicle budding and transport may be actin-myosin-mediated processes (step 5, 5a). Vesicles containing Pf EMP1 and Pf EMP3 uncoat (step 5) and are transported across the RBC cytosol to the Maurer clefts (step 6) or directly to the erythrocyte plasma membrane (step 6a) by an actin-myosin-mediated process. Pf NSF associates with the vesicles prior to their interaction with the clefts or the erythrocyte plasma membrane. Vesicles could be transported along actin-tethered Maurer clefts to the RBC membrane (step 7), or vesicles could bud from the ends of the Maurer cleft and diffuse to the RBC membrane. The vesicles associate with the RBC cytoskeleton (step 8) leading to knob formation.⁹  The appearance of extended chains of vesicles in the RBC cytosol and at the RBC membrane in IRBCs treated with AlF suggests an AlF-sensitive factor (eg, small GTPases such as Pfsar1p and/or Pf Rabs) may prevent vesicle uncoating (step 5) and block vesicle fusion at the clefts and/or erythrocyte plasma membrane, respectively, causing the vesicles to backup into chains.