Figure 12.

Model for the transport of Tacfurin and the mutant construct Tac-furin/ADA. Both constructs are internalized from the plasma membrane and initially enter sorting endosomes (SE). Tac-furin is then retained in the sorting endosomes as they mature into late endosomes (LE). Shortly after the endosomes lose the characteristics of sorting endosomes, Tac-furin is delivered from the maturing endosomes into the TGN. This may occur in the maturing endosome/endosome carrier vesicle (Gruenberg and Maxfield, 1995). In contrast, Tac-furin/ADA is removed rapidly from sorting endosomes and transported to the ERC. Although a portion of the mutant construct is recycled back to the cell surface, the rest is delivered to the TGN as is the case for TGN38. Black arrows represent steps of protein traffic that exist, but are not followed by Tac-furin nor Tac-furin/ADA. The stippled TGN-PM arrow represents decreased retrieval of Tac-furin/ADA from the TGN to the PM.