FIGURE 7.

Multiple distinct translocons act in apicoplast protein import. a, Der1, Cdc48, and Ufd1 are believed to be core components of the translocon of the ERAD pathway. b, duplication of the Der1 gene in the algal endosymbiont and relocation of its protein product to its plasma membrane enables c, protein import from the host endomembrane system. d, schematic representation of trafficking of nuclear-encoded proteins to the lumen of the apicoplast comparing a model employing subsequent Der1, Toc, and Tic translocons with a model in which the Toc translocon has been subsequently replaced by a second Der1 translocon. Cargo proteins are shown in yellow. The transit peptide (purple) is cleaved upon arrival. Note that trafficking of certain apicoplast membrane proteins appears not to require a bipartite signal sequence (26) and might occur through a different mechanism.